Detector remodulator and optoelectronic switch

ABSTRACT

A silicon-on-insulator chip including an arrayed waveguide grating (AWG) and an array of detector remodulators (DRMs) in a planar arrangement with the AWG such that the modulators or modulators and detectors of said DRMs are located within the same plane as the waveguides of the AWG; and wherein each DRM is located at an input or output of the AWG.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a National Phase Patent Application and claimspriority to and the benefit of International Application NumberPCT/GB2015/050520, filed on Feb. 24, 2015, which claims priority to andthe benefit of British Patent Application Number 1403191.8, filed onFeb. 24, 2014, U.S. Provisional Patent Application No. 62/057,818, filedon Sep. 30, 2014, and British Patent Application Number 1420064.6, filedon Nov. 11, 2014, the entire contents of all of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a silicon-on-insulator chip, moreparticularly to a silicon-on-insulator chip including an arrayedwaveguide grating (AWG) and an array of detector remodulators (DRMs).

BACKGROUND OF THE INVENTION

In optical communications and optical switching it is well known thatsignals can be transposed from a first optical signal of a first channelor wavelength to a second optical signal of a second channel orwavelength.

A detector remodulator may be used to convert the first optical signalto the second optical signal and involves the detection of the firstsignal in which the first (modulated) signal is converted into anelectrical signal, followed by the modulation of light of a second(unmodulated) wavelength/channel by the (modulated) electrical signal.Whilst in the electrical domain, the signal may advantageously beprocessed, for example by one or more of amplification, reshaping,re-timing, and filtering in order to provide a clean signal to beapplied to the second wavelength/channel. However, currently in the art,to amplify and filter the electrical signal at high data rates with lownoise, the circuitry must be contained in a separate electronic chip,which requires packaging and mounting thereby increasing size and costand reducing power efficiency.

In U.S. Pat. No. 6,680,791 an integrated chip is provided with a lightdetector and modulator positioned close together so that the electricalconnection between the detector part and the modulator part is short andof low resistivity. However a maximum of only 10 Gb/s data speed ispredicted for this structure due to diode capacitance and thin-filmresistance limitations [O. Fidaner et al., Optics Express, vol. 14, pp.361-368, (2006)].

U.S. Pat. No. 6,349,106 describes a tunable laser, driven by a circuitwith a signal derived from a first optical wavelength. However becauseit comprises a III-V-material photonic integrated circuit and involvesthe use of epitaxial heterostructures and a vertical p-i-n diodestructure, is inflexible in its design and therefore inadequate for newapplications involving increasing switching speeds, reduced latency,reduced power consumption and the demand for lower cost and high-yieldmanufacturability. In particular, because the semiconductor devicesincluding the modulator built upon the semiconductor chip are driven bycircuits completed between contacts on the top surface and a contactcovering all or a large proportion of the base or underside of the chip,the capacitance of the device cannot be readily controlled by designfeatures built into the structures such as doped regions and metalcontacts.

Application of arrayed waveguide gratings (AWGs) in optical switching(including optical circuit switching and optical packet switching) hasbeen slow despite the advantages that AWGs may provide. This is in partdue to disadvantageous features of AWGs such as the uneven responseacross a range of wavelengths, cascading effects of limited bandwidthafter multiple passes as well as cross-talk between different ports.

Use of AWGs in optical switching is known; Ye et al (IEEE/ACMTransactions on Networking, VOL PP, Issue 99, Page 1, February 2014) andby Bregni et al (IEEE Journal on Selected Areas in Communications, VOL21, No 7, September 2003). Ye et al describes the use of AWGs inClos-type optical switches and other architectures and Ngo et al(Proceedings 23rd Conference of IEEE Communications Soc, 2004) hasillustrated AWG switch architectures that are rearrangeably non-blockingand strictly non-blocking.

One of the difficulties in realising optical switches is speed andanother is latency. Poor latency is especially undesirable in uses suchas high performance computing and datacenter switching where it isdesirable to make calls or rapid data exchanges on a system as close toreal time as possible.

SUMMARY OF THE INVENTION

The present invention aims to address these problems by providing,according to a first aspect, a silicon-on-insulator chip including anarrayed waveguide grating (AWG) and an array of detector remodulators(DRMs) in a planar arrangement with the AWG such that the modulators ofsaid DRMs are located within the same plane as the waveguides of theAWG; and wherein each DRM is located at an input or output of the AWG.

The modulators and the detectors of said DRMs are located within thesame plane as the waveguides of the AWG; and wherein each DRM is locatedat an input or output of the AWG.

According to a second aspect there is provided, a detector remodulatorcomprising a silicon on insulator (SOI) waveguide platform including: adetector coupled to a first input waveguide; a modulator coupled to asecond input waveguide and an output waveguide; and an electricalcircuit connecting the detector to the modulator; wherein the detector,modulator, second input waveguide and output waveguide are arrangedwithin the same horizontal plane as one another; and wherein themodulator includes a modulation waveguide region at which asemiconductor junction is set horizontally across the waveguide.

The modulation region may be a phase modulation region or an amplitudemodulation region.

The horizontal plane should be understood to be any plane parallel tothe plane of the substrate surface. The semiconductor junction should beunderstood to correspond to any one junction or number of junctionsbetween different regions having different semiconductor Fermi energiesthereby forming an opto-electronic region. The semiconductor junctionmay or may not include an intrinsic region.

The semiconductor junction is horizontal in that the junction is formedby a first doped region at (and/or extending into) one side of thewaveguide and a second doped region at (and/or extending into) theopposite side of the waveguide. All doped regions of the semiconductorjunction therefore lie along the horizontal plane defined by thedetector, modulator, second input and output waveguides.

The planar arrangement of the detector remodulator, and in particularthe horizontal junction, enables increased flexibility in both designand fabrication as the location of doped sections at either side of thewaveguide rather than above or below the waveguide gives rise to agreater degree of freedom in terms of their size and shape.

The horizontal junction configuration also enables easy access to eachof the junction regions. This is particularly useful where the junctionincludes an intrinsic region (or a third doped region) between two dopedregions as it enables electrodes corresponding to each of the threeregions to be positioned on top of the respective region.

As the detector remodulator of this invention has a horizontal junctionconfiguration, properties such as size of the doped regions can easilybe adapted and controlled during design and manufacture, parameters suchas capacitance that crucially affect the speed of operation cantherefore be controlled.

In their planar configuration, the detector, modulator, electricalcircuit, input waveguide and output waveguide form an SOI planarlightwave circuit (SOI-PLC). Silicon on insulator is a practicalplatform for the construction and integration of optical devices. Use ofbulk semiconductor SOI and SOI-compatible materials in such a PLCtechnology as opposed to III-V heterostructure semiconductor photonicintegrated circuit technology allows for integration of detectors andmodulators without the low manufacturing yields associated withepitaxial re-growth of multiple heterostructures. Optional features ofthe invention will now be set out. These are applicable singly or in anycombination with any aspect of the invention.

The first input waveguide, which is coupled to the input of thedetector, is preferably also arranged to lie within the same horizontalplane as the detector, modulator, second input waveguide and outputwaveguide.

The semiconductor junction of the modulation region may be a p-njunction and may, for each modulator embodiment described, include 2doped regions (p-n); 4 doped regions (p+, p, n, n+); or even 6 regions(p++, p+, p, n, n+, n++).

This p-n junction may further comprise a first and second electrode, thefirst electrode located directly above the p-doped region of the p-njunction and the second electrode located directly above the n-dopedregion of the p-n junction.

The semiconductor junction of the modulation region may be a p-i-njunction.

The p-doped and n-doped regions are therefore located at either side ofthe waveguide with an intrinsic region between. The doped regions mayextend into the waveguide such that the width of the intrinsic region isless than the width of the waveguide.

The p-i-n junction may further comprise a first, second and thirdelectrode, the first electrode located directly above the p-doped regionof the p-i-n junction, the second electrode located directly above then-doped region and the third electrode located directly above theintrinsic region of the p-i-n junction.

Electrodes are preferably metal strips which lie above the relevantdoped region along its length. In this way, an electric bias can beapplied to the relevant doped region via the electrode located above it.

In general the electrodes should be small and the doped regions, withinsemiconductor junctions (p-n, p-i-n, or otherwise) should be small.

The width of the doped regions taken along the horizontal plane and in adirection perpendicular to the longitudinal (or circumferential) axis ofthe doped waveguide is particularly important.

For example, in a single semiconductor junction such as a p-n junction,the total width of either the p-doped or n-doped region may be no morethan 20 μm. Where the p doped region is graded into differentsub-regions (for example in that it contains p, p+ and p++ regions),each sub-region may have a width of no more than 15 μm, but the width ofdifferent sub-groups may be substantially different to each other, forexample the p doped region may be larger than each of the p+ and the p++regions. In order to further improve on modulation and detector speeds,each sub-region may have a width no more than 10 μm, 5 μm, 2 μm, 1 μm,0.5 μm or even 0.3 μm.

Although the sizes above are described in relation to p doped regions,they would equally apply to n doped regions.

Furthermore, where the modulator or detector waveguide includes asemiconductor-intrinsic-semiconductor junction (e.g. a p-i-n junction),each doped region may have a width taken along the horizontal plane andin a direction perpendicular to the longitudinal (or circumferential)axis of no more than 15 μm, or in order to further reduce the speed ofoperation, a width of no more than 10 μm, 5 μm, 2 μm, 1 μm, 0.5 μm oreven 0.3 μm.

Electrodes which apply a bias to a doped region will preferably have awidth which is less than the width of that doped region. Depending onthe size of the relevant doped region, the electrode may therefore havea width of no more than 10 μm, or in order to further reduce the speedof operation, a width of no more than 5 μm, 2 μm, 1 μm, 0.5 μm or even0.3 μm.

The ridge width for the waveguides of the detector or modulator regionsmay be 0.3-1 μm or preferably 0.45-0.9 μm and the slab height of thedetector or modulator regions may be 0-0.4 μm, preferably 0.05-0.035 μm.The silicon overlayer thickness may be 0.2-3.5 μm, preferably 0.2-3.2μm.

The amplitude or modulation region of the modulator is preferably formedfrom a bulk semiconductor material.

Preferably, the detector also comprises a waveguide portion with asemiconductor junction set horizontally across the waveguide.

Doped sections of the detector are therefore also located at either sideof the waveguide rather than above and below the waveguide.

The semiconductor junction of the detector may be a p-i-n junction. Aswith the p-i-n modulator, the p-doped and n-doped regions are located ateither side of the waveguide with an intrinsic region between.

Alternatively, the semiconductor junction of the detector may be ann-i-n, n-p-n or p-i-p junction such that the detector functions as aphototransistor. In this way, the detector itself provides a gain whilstavoiding the need for separate components which provide gain butundesirably increase resistance. Avoiding the need for opticalamplifiers to amplify the optical input signal is also advantageousbecause optical amplifiers (such as a semiconductor optical amplifier,SOA) add noise to the optical signal and also draw significantadditional electrical power as well as adding cost and complexity to theSOI platform. An alternative to optical amplifiers is electricalamplification of the received input signal. However, unless atransimpedance amplifier (TIA) is used, a high transimpedance resistancecircuit is needed which disadvantageously prevents high speed operation.

Each of the n-i-n, n-p-n or p-i-p doping structures may provide adifferent amount of electrical gain and/or electrical bandwidth;Typically the higher the gain of the design, the lower the electricalbandwidth.

The photodetector is preferably formed from a bulk semiconductormaterial.

The electrical circuit may be a single strip of metal or a few strips ofmetal placed in series and/or in parallel with each other to form asimple RF circuit. In this way, the electrical circuit is reduced incomplexity. A detector remodulator with such an electrical circuit ispreferable where the received optical input signal has travelled overshort distances and so does not incur heavy optical impairments. In suchcases only amplification of the signal may be desired as the signal mayhave degraded in intensity. However, the amount of jitter or amplitudeadded should not be significant, so there should be no need to reshapeor retime the signal.

The length of the electrical circuit from its electrical connection atthe detector to its electrical detector at the modulator may take anyvalue from 1.0 to 2×10⁴ μm. Where the electrical circuit is keptadvantageously small to increase speed, it may be no more than 10 μm,within the range of 1.5 μm to 10 μm, or even no more than 1.5 μm. Theelectrical circuit will be as wide and as thick as practically possible(for example 5.0-50 μm).

The electrical circuit may contain one or more resistors and the one ormore resistors may include a variable resistor.

The electrical circuit may include nonlinear circuit elements (e.g.transistors) configured to amplify the electrical signal which forms aninput to the modulator with a high speed circuit and/or limit theelectrical signal in such a way that the signal does not drop below aminimum magnitude and/or above a maximum magnitude.

The electrical circuit may be monolithic. In this way, all of themanufacturing of the DRM is carried out in the semiconductor fabricationprocess. Only extra fabrication process steps are required.

The electrical circuit may be a stripline circuit. In this way, thefabrication of the electrical circuit is simplified and therefore morecost-effective than alternative circuits, requiring only application ofa mask and a metallisation process. This type of electrical circuit ismost suitable where the electrical circuit itself has a simple structuresuch as a single strip of metal or a few strips of metal. Again onlyextra fabrication process steps are required here.

The electrical circuit may be surface mounted. This type of electricalcircuit is particularly useful when the circuit includes components suchas transistors, filters and/or additional nonlinear components. Suchcomponents cannot be added as part of a stripline circuit.

The modulator may be an electro-absorption modulator (EAM). This type ofmodulator is advantageously simple and provides relatively highmodulation speeds.

The EAM modulator is preferably formed of SiGe.

Alternatively, the modulator is a Mach-Zehnder Modulator (MZM). Thistype of modulator is advantageous over an EAM because it is capable offunctioning over a larger wavelength bandwidth. In addition, there maybe no need to engineer the material of the modulator such that it has aprecise band-gap wavelength. In other modulators for example EAMmodulators, control of SiGe composition is required, which may includeincorporation and epitaxial growth of Ge or SiGe. The homogeneoussilicon embodiment in particular is easier to fabricate.

On the other hand, the overall length of the device is longer and higherinsertion losses mean that the MZM can be less power efficient than theEAM. In addition, this modulator requires a more complicated p-n dopingstructure with many more doping regions; and a more complicatedelectrical circuit in the form of a phase-matched and impedance matchedRF driving circuit. An RF drive circuit which can reach operationalspeeds of 25 GHz and greater is not straightforward.

Furthermore, the MZM has a larger device size compared to othermodulators and the MZM requires an additional fine tuning region tomatch the laser wavelength to the pass-band wavelength for the ‘on’state.

Preferably, each arm of the MZM includes a modulation region (e.g. anamplitude or a phase modulation region). Each modulation region has ahigh operation speed (i.e. an operation speed of 25 Gb/s with a 3-dBbandwidth of 15 or more GHz).

Preferably, each arm of the MZM includes a phase shift region inaddition to the modulation region and the phase shift region preferablyhas a lower speed than the modulation regions.

The phase shift region may comprise a p-i-n junction such that itoperates by way of carrier injection. On the other hand, the phase shiftregion may comprise a p-n junction such that it operates by way ofcarrier depletion.

Phase shift regions may be low speed as their function is cavity FSRfine tuning. In this way, they provide a means of operating wavelengthfine tuning as well as thermal drift compensation.

The modulation regions may be homogeneous silicon or may be silicongermanium.

The Mach-Zehnder modulator may be single-drive or may be dual-drive andmay be a push/pull Mach-Zehnder modulator. Where a push/pullconfiguration is used, lower driving voltages are required in each arm.

According to an alternative embodiment, the modulator may be aFabry-Perot resonator modulator.

The Fabry-Perot (F-P) resonator modulator may be formed in a singlewaveguide section by two reflectors in series with one or moremodulation regions (e.g. phase modulation regions or amplitudemodulation regions) between the two reflectors.

In this way, the use of an IIR filter means that the effect of therefractive index change induced by the modulation regions is enhanced bythe increased number of round trips in the resonator cavity. Wheremodulation is carried out by carrier injection, a smaller injectedcurrent density is required to perform modulation with a givenextinction ratio. Where modulation is carried out by carrier depletion,a smaller bias voltage is required to perform modulation with a givenextinction ratio. Thus in a DRM less optical or electrical amplificationis needed to perform modulation (as compared to the EAM or MZMembodiment). The F-P can also work over a larger bandwidth with the useof fine tuning.

On the other hand, the fabrication and design complexity of theFabry-Perot embodiment is greater due to incorporation of the DBRgratings or reflectors. With increasing high speeds of the modulator (25or 40 Gb/s), the manufacturing complexity and tolerances increase. Inaddition, the photon lifetime of the cavity must be kept optimally lowwhich means that the cavity length must be short and the Finessesufficiently low.

Furthermore, F-P modulators and IIR resonators in general are moresensitive to temperature so require active fine tuning of wavelength.

As with previous embodiments, the modulation region may be homogeneousSi or SiGe.

The reflectors of the Fabry-Perot resonator modulator may be DBRgratings and broadband DBR gratings with short lengths and deep etchdepths are preferable. Each DBR reflector could take the form of just asingle line broadband partial reflector (i.e. each could contain justone grating line per reflector, that is to say, a single waveguidedefect).

The DBRs preferably have equal reflectance over the operating bandwidthof modulator. The reflective values of the gratings are chosen to give aFinesse value that is large enough to create enough cavity round tripsto enhance the effect of Δn to sufficiently reduce the amount of drivecurrent or drive voltage needed to perform the modulation with thedesired extinction ratio, but small enough to give a cavity lifetimethat is less than 1/(bit period).

The Fabry-Perot resonator cavity may include a phase shift region inaddition to the modulation region, wherein the phase shift region has alower speed than the modulation regions.

As with other modulator embodiments described herein, the phase shiftregion provides a means for cavity FSR tuning and may comprise a p-i-njunction or may comprise a p-n junction.

According to another alternative embodiment, the modulator is a ringresonator.

As compared to Fabry-Perot modulators, ring resonator modulators areadvantageously simpler to fabricate, but have tighter fabricationtolerances.

In addition, thermal tuning (heater pads) are preferably required forfine tuning ring resonators themselves are well known in the art. Thering resonator modulator preferably comprise a ring resonator with asemiconductor junction forming an opto-electronic region and, as withprevious modulators described above, the semiconductor junction may be ap-n phase tuning region. In this way, the ring resonator is capable offunctioning as a modulator by the application of a bias across the p-njunction.

The actual boundary where the p- and n-doped regions of the p-n junctionmeet is preferably circular and lies along or near the centre of thewaveguide track equidistant from the inner and outer waveguide ridges.The n-doped region may be located on the inside of the ring waveguideincluding the inner half of the ring waveguide itself but also extendinginwardly beyond the inner waveguide ridge. The p-doped region may belocated on the outside of the ring waveguide, including the outer halfof the ring waveguide but also extending outwards beyond the outerwaveguide ridge.

In an alternative embodiment, the p-doped region may be located on theinside of the ring waveguide (including the inner half of the ringwaveguide itself but also extending inwardly beyond the inner waveguideridge) and the n-doped region may be located on the outside of the ringwaveguide (including the outer half of the ring waveguide but alsoextending outwards beyond the outer waveguide ridge).

Optionally, the ring resonator comprises a ring-shaped waveguide; afirst straight waveguide to couple light into the ring-shaped waveguide;and a second straight waveguide to couple light out of the ring-shapedwaveguide. In this case, the transmittance spectrum will form a periodicset of peaks, each peak separated from the adjacent two peaks via awavelength difference proportional to the free spectral range (FSR) ofthe ring resonator.

Optionally, the ring resonator comprises a ring-shaped waveguide and asingle straight waveguide to couple light both into and out of thering-shaped waveguide. In this case, the transmittance spectrum willform a periodic set of sharp troughs, each trough separated from the twodirectly adjacent troughs via a wavelength difference proportional tothe free spectral range (FSR) of the ring resonator. As thistransmittance spectrum is the inverse of that for the “dual straightwaveguide” embodiment, such an arrangement will require an oppositedrive signal (bias to be applied across the p-n junction) as compared tothe single coupled waveguide version in order to give rise to the samemodulation effect.

Where the ring resonator includes first and second coupling waveguidesthe first straight waveguide is located at one side of the ring-shapedwaveguide and the second straight waveguide is located at the oppositeside of the ring-shaped waveguide.

Regardless of the mechanism for coupling light in and out of the ringwaveguide, the ring resonator modulator preferably includes a finetuning region in addition to the semiconductor junction. This finetuning region may be a heater for thermal tuning. Such heaters appliedto ring resonators are known in the art (see Dong et al. Optics Express,vol. 18, No. 11, 10941, 24 May 2010).

Alternatively, the fine tuning region may include an additionalsemiconductor junction incorporated into the resonator (i.e. in additionto the p-n junction which controls the high speed modulation).

The ring resonator coupled to two straight waveguides is advantageousover the embodiment with one single straight waveguide in that it doesnot invert the drive signal (high voltage is ‘on’). In addition, becauseon-resonance gives high transmission, the ring resonator requires lessvoltage swing for good extinction ratio. However, the addition of asecond straight waveguide increases the complexity of the fabrication aswell as increasing the amount of metal crossing over the waveguide,therefore increasing not only the optical loss of the working device,but also the potential for complications during fabrication.

In all embodiments, a semiconductor optical amplifier (SOA) may belocated within the waveguide platform before the input waveguide whichcouples light into the detector.

According to a third aspect of the present invention, there is provideda detector remodulator for use in a silicon on insulator waveguideplatform, the detector remodulator including: a detector; a modulatorand an electrical circuit connecting the detector to the modulator;wherein the modulator is a ring resonator modulator.

According to a fourth aspect of the present invention, there is provideda method of manufacturing a detector remodulator on a silicon oninsulator platform, the method including the steps of: providing adetector and a first input waveguide which is coupled to the detector;providing a modulator comprising a waveguide having an electro-opticalregion, a second input waveguide which is coupled to the modulator, andan output waveguide which is also coupled to the modulator; andproviding an electrical circuit which electrically connects the detectorto the modulator; wherein the detector, modulator, input waveguides andoutput waveguide are all located within the same horizontal plane as oneanother; the method further comprising the step of generating a firstdoped region at one side of the waveguide and a second doped region atthe opposite side of the waveguide, the first and second doped regionforming a semiconductor junction set horizontally across the modulatorwaveguide.

The size of the doped regions may be chosen to optimise speed of thedevice.

The method may further comprise the steps of providing the featuresdescribed herein in relation to one or more embodiments of the secondaspect.

Further optional features of the invention are set out below.

According to a fifth aspect of the present invention, there is providedan optoelectronic packet switch comprising: one or more switch input(s)for receiving optical packet signals; a passive optical router havinginput ports and output ports, the optical paths between which arewavelength dependent; a switch control unit; and a plurality of detectorremodulators (DRMs) configured to receive optical signals from the oneor more switch input(s) and to generate modulated optical signals fortransmission to the input ports of the passive optical router, eachdetector remodulator (DRM) comprising: one or more detectors forconverting an optical packet signal received at the one or more switchinput(s) into an electrical packet signal; one or more modulators forgenerating the modulated optical signals, each modulator configured to:receive a wavelength tuned laser input from a tunable laser; receive theelectrical packet signal from one of the detectors; and to generate amodulated optical signal at the tuned wavelength, the modulated opticalsignal containing the information of the electrical packet signal andthe tuned wavelength chosen to select a desired output port of thepassive optical router for the modulated optical signal; and anelectronic circuit connecting the detector to the modulator; whereineach of the one or more modulators is a separate component from thetunable laser which provides its wavelength tuned laser input; andwherein the switch control unit includes a scheduler which iscommunicably connected to the electronic circuit of each DRM; theelectronic circuit configured to control the generation of the modulatedoptical signal by the modulator based on scheduling information receivedfrom the switch control unit. This control of the generation of themodulated optical signal may include both control of the modulator andcontrol of the carrier wavelength of the resulting modulated opticalsignal.

In this way, the electronic circuit may include a modulator driver fordriving the modulator and a laser wavelength tuner for driving theseparate tunable laser. In addition to the scheduler, the switch controlunit may also include a central processing unit (CPU) which may performadditional switch control functions.

The electronic circuit may be configured to perform any one or more ofthe following functions: deciding the wavelength for the tuned laser;deciding the timing at which to send a specific packet through thepassive optical router relative to other packets; deciding themodulation rate of the modulated optical signal; and deciding whichmodulation protocol should be used.

The process of deciding the wavelength may involve a scheduler fordetermining the route of a particular packet signal and this schedulermay be located in the switch control unit external to the electroniccircuit. The electronic circuit may therefore be configured to receivethe information from the scheduler and to control the wavelength of thetunable laser based on this information.

According to a sixth aspect of the present invention, there is provideda detector remodulator (DRM) comprising: one or more detectors forconverting an optical packet signal into an electrical packet signal;one or more modulators, each modulator configured to: receive awavelength tuned laser input from a tunable laser; receive an electricalpacket signal from one of the detectors; and to generate a modulatedoptical signal at the tuned wavelength, the modulated optical signalcontaining the information of the electrical signal; and an electroniccircuit connecting the detector and modulator, the electronic circuitcontaining means for controlling the generation of the modulated opticalsignal based on scheduling information from an external control unit;wherein the modulator is separate component from the tunable laser.Again, the control of generation of the modulated optical signal mayinclude both control of the modulator and control of the wavelength ofthe resulting modulated optical wavelength.

One or more of the DRMs of the optoelectronic packet switch of thefourth embodiment may therefore correspond to the DRM(s) of the fifthembodiment.

By “separate component” it is envisaged that the modulator may take anyform which is exterior to the tunable laser component. This may take theform of a modulator chip which abuts a tunable laser chip or may takethe form of a modulator which is physically separated from the tunablelaser chip. The modulator and tunable laser may be monolithicallyintegrated but yet physically separated on the floor plan. Theoptoelectronic packet switch of the present invention enables fasterswitching speeds to be reached as compared to alternatives in whichmodulation is carried out within the cavity of the tunable laser itselfthat is, within the cavity created by the reflecting mirrors of thelaser.

The modulator of each of the DRMs of the optoelectronic packet switchmay take the form of any one of or any combination of the modulatorsdescribed in this application. For example, the modulator may be anelectro-absorption modulator, a Mach-Zehnder modulator, a Fabry-Perotresonator modulator, or a ring-resonator modulator, and may include amodulation region at which a semiconductor junction is set horizontallyacross the waveguide, and the modulator region may take the form of: anelectro-absorption material; or phase-shift region(s) inside aMach-Zehnder modulator; a Fabry-Perot resonator cavity; or aring-resonator.

The electronic circuit of one or more of the DRMs may include a packetprocessor. In this way, header processing of the electrical packetsignals generated by the detector is carried out within the DRM.

Alternatively or in addition, the switch control unit may include apacket processor, in this way header processing of the electricalpackets generated by the detector may be carried out outside of the DRMin the switch control unit. Where packet processing is carried out inthe switch control unit, only a portion of the packets may be sent fromeach of the DRMs of the optoelectronic switch to the switch control unitand the processing carried out using just these portions. This enablesthe amount of data required to be sent and received by the DRM to bereduced.

The electronic circuit of the DRM may be configured to transmitinformation about each electrical packet signal to the scheduler. It mayalso be configured to receive control information from the scheduler.

The electronic circuit of the DRM may include a wavelength tuner whichcontrols the wavelength of the wavelength tuned laser input based oninformation received from the switch control unit. In this way, nocontrol of the tunable laser is required outside of the DRM.

The electronic circuit of each DRM may additionally be configured toinclude a buffer for electrical packet signals. This buffering may becarried out in an SRAM module within the DRM, such an SRAM module beinglocated in-between the detector and the modulator and in communicationwith any signals sent from the switch control unit to the DRM so thatelectrical packets corresponding to the scheduled signals are bufferedin accordance with the scheduling information.

The electrical circuit of the DRM may be an electronic circuit, forexample an Application Specific Integrated Circuit (ASIC). Thisapplication specific integrated circuit may be any multi-functional CMOSchip.

Each electronic circuit of a DRM may take the form of a CMOS chip whichmay include one or more of the following: a receiver circuit, atransimpedance circuit, gain circuitry, signal regeneration circuitry,and a modulator driver. The signal regeneration circuitry may includesignal retiming and signal reshaping.

At least a portion of the electronic circuit of each DRM may be anelectronics chip in direct contact with a photonic chip which containsthe detector and the modulator.

The electronics chip is preferably in close proximity to the detectorand/or the modulator in order to maximize the operation speed. Tomaximize speed, the electronics chip (e.g. a CMOS chip) may be speciallymounted for example, flip-chip bonded with low capacitance and lowresistance metal connections. Alternatively, the electronics chip couldbe attached on top of the silicon photonics chip via an interposer orcould be monolithically integrated.

The processor and/or other components of the DRM electronic circuit maybe integrated into the same CMOS chip as the modulator driver. Thishelps to optimise speed of the device as well as conserving real estateon the photonic chip.

The detector and the modulator may be in close proximity to one another.Preferably the electrical path between the detector and the modulator isno more than 1 cm, even more preferably, the electrical path is no morethan 1 mm, even more preferably the electrical path is no more than 100μm.

Advantageously, from the user's point of view, the optoelectronic switchappears to be “all optical” despite the fact that processing andscheduling are carried out in the electrical domain.

The detector is preferably a photodetector (e.g. a photodiode) althoughit could take the form of any receiver suitable for detecting the inputsignal. It may for example include a burst mode receiver.

The passive optical router may be an AWG such as a cyclic AWG.

The switch architecture may take the form of a Clos network.

Each DRM may be configured to split an input optical packet signal intoa plurality of separate streams which are processed by the electroniccircuit of the DRM in parallel.

Each DRM may support one or more standard protocols, for example: 1G,2.5G, 10G, 25G, 40G, 100G Ethernet, and similar rates for InfiniBand,PCI Express, SATA, and USB.

Each DRM may be configured to have a specific interface to the packetscheduler of the switch control unit. For example, the scheduler andmultiple DRMs could all be located on the same electrical circuit chip.Alternatively the scheduler and/or the electrical DRM circuit could be anetwork-on-chip standard such as ARM AMBA. Or the scheduler and theelectrical circuits of one or more of the DRMs could be physicallyseparated and connect to one another for example by way of a PCIExpress.

Each DRM may include a plurality of ports (e.g. 4 input ports and 4output ports) and will include detector-modulator pairs so that there isthe same number of detectors as there are modulators.

Each packet of data which enters a port may be split into a plurality oflanes which may be processed in parallel. The plurality of lanes may be4 or more lanes but may be any number, N of lanes. Where there are fourlanes, each lane may form a 25G stream of data.

The electronic circuit of the DRM may further comprise one or morebuffers which may be made of SRAM.

The detector and modulator of each detector remodulator may be locatedadjacent one another on a single optical chip.

According to a seventh aspect of the present invention there is provideda method of optical packet switching using a passive optical routerhaving a plurality of input ports and a plurality of output ports, themethod comprising the steps of:

-   -   providing an optoelectronic packet switch comprising: one or        more switch input(s) for receiving optical packet signals; a        passive optical router having input ports and output ports, the        optical paths between which are wavelength dependent; a switch        control unit; and a plurality of detector remodulators        configured to receive the optical input signals and to generate        modulated optical signals for transmission to the input ports of        the passive optical router;    -   receiving at one or more of the detector remodulators an optical        packet signal from the one or more switch input(s);    -   converting each optical packet signal received into an        electrical packet signal using one or more detectors of the one        or more detector remodulators;    -   receiving at the one or more detector remodulators a wavelength        tuned laser input from a separate wavelength tunable laser; and    -   generating at a modulator of the one or more detector        remodulators a modulated optical signal at the tuned wavelength,        the modulated optical signal containing the information of the        electrical packet signal and having a wavelength chosen to        result in a desired output port of the passive optical router;    -   wherein the modulator is controlled via an electronic circuit        which connects it to one of the one or more detectors and which        controls the modulation process based on scheduling information        received from the switch control unit.

The step of controlling the modulation process at the electronic circuitmay also include the step of controlling the tuned wavelength of theseparate wavelength tunable laser. This step may include determining ata scheduler in the switch control unit a route for a packet signal.Information concerning the route chosen may be sent from the switchcontrol unit and received by the electronic circuit of the detectorremodulator which then controls the wavelength of the tunable laserbased on this information.

The optional features described above in relation to the optoelectronicpacket switch of the fifth aspect and DRM of the sixth aspect may all beprovided as a step of the method of the seventh aspect.

According to an eighth aspect of the present invention, there isprovided an optoelectronic circuit switch comprising: one or more switchinput(s) for receiving optical input signals; a passive optical routerhaving input ports and output ports; a switch control unit; and aplurality of detector remodulators (DRMs) configured to receive opticalsignals from the switch input(s) and to generate modulated opticalsignals for transmission to the input ports of the passive opticalrouter, each detector remodulator (DRM) comprising: one or moredetectors for converting each optical signal received at the switchinput(s) into an electrical signal; one or more modulators forgenerating the modulated optical signals, each modulator configured to:receive a wavelength tuned laser input from a tunable laser; receive theelectrical signal from one of the detectors; and to generate a modulatedoptical signal at the tuned wavelength, the modulated optical signalcontaining the information of the electrical signal and the tunedwavelength chosen to select a desired output port of the passive opticalrouter for the modulated optical signal; and an electronic circuitconnecting each of the one or more detectors to a correspondingmodulator; wherein each of the one or more modulators is a separatecomponent from the tunable laser that provides its wavelength tunedlaser input; and wherein the switch control unit is communicablyconnected to the electronic circuit of each DRM, the electronic circuitconfigured to control the generation of the modulated optical signal bythe modulator based on control information received from the switchcontrol unit.

In this way, an optoelectronic switch is provided which behaves as anoptoelectronic circuit switch and enables faster switching speeds to bereached as compared to alternatives in which modulation is carried outin the cavity of the tunable laser itself, and as compared to otherconventional circuit switches based on other switching technologies suchas MEMS or liquid crystal.

The optional features described above in relation to the optoelectronicpacket switch of the fifth aspect and the detector remodulator of thesixth aspect are applicable to the optoelectronic circuit switch in thatoptical signals may be converted and switched in the same way as opticalpacket switches with the exception that there is no requirement for anyfeatures that are specific to packet information such as packetscheduling, packet processing, or packet buffering. Where information isnot being sent as packets, the presence of buffers is less importantalthough buffers may still be present in the electrical circuit of anoptoelectronic circuit switch in order to delay some optical signalsrelative to others to resolve contention (blocking).

According to a ninth aspect of the present invention, there is provideda silicon-on-insulator chip including the optoelectronic switch of anyone of the fifth or eighth aspect or the detector remodulator of thesixth aspect.

The passive optical router of the switch may be an arrayed waveguidegrating (AWG) located in the same optical plane as the DRMs.

In “the same optical plane” should be interpreted as each device (DRMand AWG) being located in a planar arrangement i.e. the same layer ofthe semiconductor chip such that the modulators or modulators anddetectors of said DRMs are located within the same plane as thewaveguides of the AWG; each DRM being located at an input or an outputof the AWG.

A DRM may be located at one or more inputs of the AWG and one or moreoutputs of the AWG. A DRM may be located at each input of the AWG and ateach output of the AWG.

Optionally, the signal input waveguide for one or more of the DRMs lieswithin the plane of the AWG.

Optionally, the signal input waveguide for one or more of the DRMsimpinges the modulator of the DRM from an angle to the plane of thewaveguides of the AWG.

Where the electrical circuit of the DRM is an electronic circuit, suchas an ASIC, it may be flip chip mounted onto the silicon-on-insulatorchip.

The silicon-on-insulator chip may further comprise one or more tunablelasers, each tunable laser for providing a wavelength tuned laser inputto the modulator of a respective one or more of the DRMs, the one ormore tunable lasers located on the same chip as the DRMs, the passiveoptical router, and at least a portion of the electrical circuit of theDRM.

In one arrangement, the one or more tunable lasers and the one or moreDRMs may be integrated onto a single optical chip but the passiveoptical router may form a separate component which is in opticalconnection with the inputs or outputs of the one or more DRMs.

The one or more tunable lasers may be located within the same plane asthe DRM and the AWG and the tunable laser may be thermally isolated fromthe AWG and DRM to prevent undesirable heating of the AWG and DRM by thetunable lasers.

A DRM with a tunable laser providing the wavelength tuned input lightfor its modulator may be located at each input of the AWG and/or at eachoutput of the AWG.

In one embodiment of the silicon-on-insulator chip, the chip comprises,in a planar arrangement: a first AWG having a plurality of inputs and aplurality of outputs; a first array of DRMs located at the input of thefirst AWG, each DRM in the first array having a wavelength tunable laserinput; the first array of DRMs arranged such that the output of each DRMin the first array forms an input signal for each input port of thefirst AWG; a second AWG having a plurality of inputs and a plurality ofoutputs; a second array of DRMs located at the input to the second AWG;each DRM in the second array having a wavelength tunable laser input;the second array of DRMs arranged such that the output of each DRM inthe second array forms an input signal for each input port of the secondAWG; wherein each output of the first AWG forms an input signal for arespective DRM of the second array of DRMs.

The first and second AWGs may take the shape of elongated arcs and maybe located in an end-to-end arrangement on the planar chip. In this waythe two AWGs form successive arcs which lie one after another along anelongate direction thereby enabling the chip itself to take an elongateshape.

Alternatively, the first and second AWGs may be positioned in a nestedarrangement within the plane of the waveguides. In this way, the firstarch tessellates with the second arch.

The first AWG may have a smaller arc than the second AWG; such that thefirst AWG may be nested underneath the arc of the second AWG (but stillwithin the plane of the waveguides).

In another embodiment, a single tunable laser could be configured tofeed unmodulated light for the wavelength tuned inputs into multipleDRMs.

In one embodiment, the silicon-on-insulator chip may comprise, in aplanar arrangement: a first array of DRMs; each DRM located at an inputwaveguide of the AWG, and each DRM coupled to a tunable laser whichprovides the wavelength tuned input for its modulator; a second array ofDRMs; each DRM located at an output waveguide of the AWG and each DRMcoupled to a tunable laser which provides the wavelength tuned lightinput for its modulator; an optical demultiplexer, the output of whichforms the input signals for the first array of DRMs; and an opticalmultiplexer, the inputs for which are the outputs of the second array ofDRMs.

The silicon-on-insulator chip may include an array of detectorremodulators (DRMs) in a planar arrangement with an array of tunablelasers, each tunable laser forming a wavelength tuned input of arespective DRM.

There is provided a data centre network including thesilicon-on-insulator chip or switch of any one of the previous claims.

An alternative switch is envisaged in which the interface input and/oroutput of the switch is electrical. In such a case, the detector wouldnot be required. For example, as an alternative there could be provided:a switch comprising: one or more switch input(s) for receiving inputsignals; a passive optical router having input ports and output ports,the optical paths between which are wavelength dependent;

-   -   a switch control unit; and    -   a plurality of receiver/modulation units configured to receive        electrical signals from the one or more switch input(s) and to        generate modulated optical signals for transmission to the input        ports of the passive optical router, each receiver/modulation        unit comprising:        -   one or more receivers for receiving electrical switch            input(s);        -   one or more modulators for generating the modulated optical            signals, each modulator configured to: receive a wavelength            tuned laser input from a tunable laser; receive the            electrical signal from one of the receivers; and to generate            a modulated optical signal at the tuned wavelength, the            tuned wavelength chosen to select in a desired output port            of the passive optical router and the modulated optical            signal containing the information of the electrical packet            signal; and an electronic circuit connecting the receiver to            the modulator; wherein each of the one or more modulators is            a separate component from the tunable laser that provides            its wavelength tuned laser input; and wherein the switch            control unit includes a scheduler which is communicably            connected to the electronic circuit of each            receiver/modulation unit; the electronic circuit configured            to control the generation of the modulated optical signal by            the modulator based on scheduling information received from            the switch control unit.

One advantage of all of the optoelectronic switches described herein isthe fact that no electrical switches (and therefore no transceivers) arerequired as in conventional architecture such as that shown in FIG. 14.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 shows a schematic circuit diagram of a wavelength conversion chipincluding a detector remodulator according to the present invention;

FIG. 2 shows a schematic top view of a silicon on insulator detectorremodulator comprising an EAM modulator;

FIG. 3a shows a cross sectional view of the detector remodulator takenalong the line A-B of FIG. 2 where the electrical circuit includes ametal strip;

FIG. 3b shows a cross sectional view of the detector remodulator takenalong the line A-B of FIG. 2 where the electrical circuit includes amonolithic doped conductor;

FIG. 3c shows a cross sectional view of the detector remodulator takenalong the line A-B of FIG. 2 where the electrical circuit includes amonolithic doped conductor; and

FIG. 3d shows a cross sectional view of the detector remodulator takenalong the line A-B of FIG. 2 where the electrical circuit includes asurface mounted chip;

FIG. 4 shows a schematic top view of an alternative modulator in theform of a Mach-Zehnder modulator;

FIG. 5 shows a side view of the modulator of FIG. 4 taken along the lineX-Y of FIG. 4;

FIG. 6 shows a schematic top view of an alternative modulator in theform of a Fabry-Perot resonator modulator;

FIG. 7 shows an example drawing of a transmittance spectrum for theFabry-Perot resonator modulator;

FIG. 8a shows a peak in the transmittance spectrum of the Fabry-Perotresonator tuned to the laser emission wavelength (“on state”) and FIG.8b shows a peak in the transmittance spectrum of the Fabry-Perotresonator de-tuned from the laser emission wavelength (“off state”);

FIG. 9 shows a schematic top view of an alternative modulator in theform of a ring resonator modulator;

FIG. 10 shows a side view of the ring resonator modulator of FIG. 9taken along the line M-N of FIG. 9;

FIG. 11 shows an example of a transmittance spectrum for the ringresonator modulator;

FIG. 12 shows a schematic top view of a further alternative modulator inthe form of an alternative ring resonator modulator;

FIG. 13a shows an example of a transmittance spectrum for the ringresonator modulator of FIG. 12 tuned to the laser emission wavelength(“on state”);

FIG. 13b shows an example of a transmittance spectrum for the ringresonator modulator of FIG. 12 de-tuned from the laser emissionwavelength (“off state”);

FIG. 14 shows an example of a traditional data network which useselectrical switches;

FIG. 15 shows an example of a data network including an optoelectronicswitch according to the present invention;

FIG. 16a is a schematic diagram showing: a first arrangement of DRMs ofthe present invention where DRMs are integrated with tunable lasers on asilicon-on-insulator chip and where the optical input signal impingesthe modulator at an angle to the plane of the AWG;

FIG. 16b is a schematic diagram showing: a second arrangement of DRMs ofthe present invention where the signal input waveguide for each DRM lieswithin the plane of the AWG;

FIG. 17 is a schematic diagram showing an optoelectronic switchincluding arrays of DRMs and an AWG;

FIGS. 18a to 18c show schematic diagrams of an optoelectronic switchincluding a plurality of passive optical routers configured to switch aplurality of lines of a signal in parallel.

FIG. 19 is a schematic diagram showing another optoelectronic switchincluding an array of DRMs and an AWG;

FIG. 20 is another schematic diagram showing a silicon-on-insulator chipaccording to the present invention including an array of DRMs and anAWG;

FIG. 21 is a schematic diagram showing a silicon-on-insulator chipaccording to the present invention including an array of DRMs and an AWGas well as further AWGs which function as demultiplexers andmultiplexers;

FIG. 22 is a schematic diagram of a silicon-on-insulator chip includinga first AWG and a second AWG in an end-to-end configuration;

FIG. 23 is a schematic diagram of a silicon-on-insulator chip includinga first AWG and a second AWG in a nested configuration;

FIG. 24 is a schematic diagram of a silicon-on-insulator chip includinga first AWG and a second AWG;

FIG. 25 is a schematic diagram of an example of a detector remodulator(DRM) for an optoelectronic packet switch;

FIG. 26 is a schematic diagram of an alternative example of a detectorremodulator (DRM) for an optoelectronic packet switch;

FIG. 27 is a schematic diagram of an example of a detector remodulator(DRM) for an optoelectronic circuit switch;

FIG. 28 is a schematic diagram of an optoelectronic switch according tothe present invention; and

FIG. 29 is a schematic diagram of an alternative optoelectronic switchaccording to the present invention.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES OF THE INVENTION

FIG. 1 shows a conversion chip 10 including a detector remodulator (DRM)1 according to the present invention. The detector remodulator 1comprises a silicon on insulator (SOI) waveguide platform whichincludes: a detector 2, a modulator 3 and an electrical circuit 4 whichelectrically connects the detector to the modulator. The detector 2 iscoupled to an input waveguide 5 and the modulator 3 is coupled to anoutput waveguide 6.

The detector 2, modulator 3, input waveguide 5 and output waveguide 6are arranged within the same horizontal plane as one another within theSOI waveguide platform. In the embodiment shown, a portion of theelectrical circuit is located directly between the detector and themodulator.

The conversion chip includes a waveguide for a (modulated) first opticalsignal 7 of a first wavelength λ₁. In the embodiment shown in FIG. 1,the waveguide is coupled to the input waveguide 5 of the detector 2 viaa first and second optical amplifier 71, 72, although in an alternativeembodiment (not shown) the first optical signal may be directly coupledto the input waveguide 5 of the detector. The detector converts themodulated input signal into an electrical signal which is then appliedto the modulator via the electrical circuit 4.

The conversion chip also includes a waveguide for an unmodulated opticalinput 8 corresponding to a second wavelength λ₂. This waveguide iscoupled to an input waveguide 9 of the modulator 3 via an opticalamplifier 81 (although may alternatively be directly coupled to inputwaveguide 9). The input waveguide 9 of the modulator also forms a partof the DRM and is oriented along the horizontal plane which includes thedetector and modulator as well as the detector input waveguide andmodulator output waveguide.

The electrical signal from the electrical circuit 4 will modulate the(unmodulated) optical input 8 thereby generating a modulated opticalsignal of the second wavelength λ₂ which is outputted by the modulatorvia the modulator output waveguide 6. This modulated output of thesecond wavelength may then me amplified via an optical amplifier 61coupled to the modulator output waveguide 6.

A power monitor may be present (not shown).

Examples of detectors, electrical circuit components and modulators thatcan form part of embodiments of the DRM 1 shown in FIG. 1 are describedbelow in relation to FIGS. 2 to 12 where like reference numbers are usedto refer to features described above in relation to FIG. 1.

FIG. 2 shows a top view first embodiment of a DRM 21 in which themodulator 23 is an electro-absorption modulator (EAM). The DRM 21 ofFIG. 2 includes a detector 22, modulator 23 and electrical circuit, aportion of which 24 is located between the detector and the modulator.

The detector 22 is made up of a bulk semiconductor material, in thiscase germanium, and includes waveguide portion 25 across which thesemiconductor junction of the detector is set horizontally. Thehorizontal semiconductor junction of the detector 22 is made up of threeregions: a first doped region 26 a, a second doped region 26 b and athird region 26 c between the first and the second doped regions. Thisthird region may be an intrinsic region or may also be doped.

In the variation of this embodiment shown in FIG. 2 (and labelled asoption a)), the first region is an n-type region; the second region is ap-type region; and the third region is an intrinsic region, such thatthe semiconductor junction of the detector 22 is a p-i-n junction.

In other variations, the first, second and third regions may insteadform a p-i-p; n-i-n or n-p-n junction (as shown as options b)-d) in FIG.2). In each of these three variations, the detector functions as aphototransistor.

In the embodiment shown in FIG. 2, the first doped region (in this casea p-type region) 26 a is located at one side of the waveguide 25 of thedetector and extends into the waveguide past the waveguide walls. Thesecond doped region (in this case an n-type region) 26 b is located atthe opposite side of the waveguide to the first region and also extendsinto the waveguide 25 of the detector. The third region 26 ccorresponding to the intrinsic part of the p-i-n junction therefore hasa width along the horizontal plane which is less than the width w of thewaveguide of the detector.

A first electrode for applying a bias to the first doped region islocated above the first doped region, a second electrode for applying abias to the second doped region is located above the second dopedregion, and a third electrode for applying a bias to the third region islocated above the third region. In all three cases, the electrodes arelocated directly on top of the relevant doped region.

The electro-absorption modulator 23 of the DRM also has a modulationwaveguide region in the form of an amplitude modulation region at whicha semiconductor junction is set horizontally across the waveguide. Themodulator 23 is made up of a bulk semiconductor material, in this casedoped silicon germanium (SiGe), and includes waveguide portion 28 acrosswhich the semiconductor junction of the detector is set in horizontally.The horizontal semiconductor junction of the modulator 23 is made up ofthree regions: a first doped region 27 a, a second doped region 27 b anda third region 27 c between the first and the second doped regions.

In the embodiment shown, the first doped region (in this case a p-typeregion) 27 a is located at one side of the waveguide 28 of the modulatorand extends into the waveguide past the waveguide walls. The seconddoped region (in this case an n-type region) 27 b is located at theopposite side of the waveguide to the first region and also extends intothe waveguide 28 of the detector. The third region 27 c corresponding tothe intrinsic part of the p-i-n junction therefore has a width along thehorizontal plane which is less than the width of the waveguide of themodulator.

In an alternative embodiment (not shown) the doped region may include aplurality of doped regions (e.g. a total of 5 regions including p+, p,intrinsic, n and n+, or even a total of 7 regions including p++, p+, p,intrinsic, n, n+ and n++).

A semiconductor optical amplifier (SOA) is located within the waveguideplatform before the input waveguide which couples light into thedetector.

The modulator 23 includes a first waveguide transition region 244between the modulator input waveguide 9 and the modulation waveguideregion at which the semiconductor junction is set horizontally acrossthe waveguide. The modulator also includes a second transition region245 between the modulation waveguide region and the modulator outputwaveguide 6.

At the first transition region 244, the waveguide height and/or widthare reduced from larger dimensions to smaller dimensions, and at thesecond transition region 245, the waveguide height and/or width areincreased from smaller dimensions to larger dimensions. In this way, thewaveguide dimensions within the modulator are smaller than those of theinput and output waveguides. This helps to improve the operation speedof the modulator (although it does so at the expense of higher losses).

The detector 22 includes a transition region 243 between the inputwaveguide 5 of the detector and the actual waveguide of the detector atwhich the height and/or width of the waveguide are reduced from largerdimensions to smaller dimensions. In this way, the waveguide dimensionswithin the detector are smaller than the input waveguide which helps toimprove the operation speed of the detector.

A portion of the electrical circuit 24 is located between the seconddoped region of the detector and the first doped region of the modulatorforming an electrical connection between the detector and the modulator.Cross sectional views of different configurations for this connectingportion taken through line A-B of FIG. 2 are shown in FIGS. 3a-3d . Inthe configuration shown in FIG. 3a the connecting portion of theelectrical circuit is stripline circuit 221 in the form of a metalstrip, the metal strip extending from the electrode on top of the seconddoped region of the detector to the electrode on top of the first dopedregion of the modulator. The second doped region of the detector and thefirst doped region of the modulator are separated by a given distance d,and the in-plane space between the detector and modulator doped regionscan be kept as silicon or Ge or SiGe or can be filled with insulatingdielectric material 225 such as SiO2. The metal strip forms a connectionabove this insulating filler.

In the variations shown in FIGS. 3b and 3c , the electrical circuit is amonolithic doped conductor 222, 223. This conductive layer may extendthe entire depth of the platform thickness down to the box level (i.e.t-h) as shown in FIG. 3b or may extend for only part of the platformthickness as shown in FIG. 3c , in which case an insulating layer 226 islocated underneath the monolithic layer. In another variation shown inFIG. 3d , the connecting portion of the electrical circuit 224 is asurface mounted chip such as an Application Specific Integrated Circuit(ASIC) in which case, conductive pads are located on the platform suchthat they match up with the pins of the chip.

As can be seen from the cross sections in FIGS. 3a-3d , the dopedregions extend into the detector waveguide and modulator waveguide anddo so throughout the entire ridge height h of the waveguides.

An alternative modulator is described below in relation to FIGS. 4 and5. This modulator can replace the EAM in the embodiment shown in FIG. 2to form an alternative DRM according to the present invention, where theremaining features and options of the DRM (other than the EAM) describedin relation to FIG. 2 still apply. In this alternative DRM embodiment,the modulator is a Mach-Zehnder modulator 33.

The Mach-Zehnder modulator is made up of two waveguide branches forminga first interferometric arm 31 and a second interferometric arm 32; eacharm including one or more phase shift modulation regions. In fact, inthe embodiment shown, each arm contains a plurality of phase shiftmodulation regions 311, 312, 321, 322 (two of which are shown in eacharm) as well as an additional phase shift region 313, 323.

Each modulation region is a phase modulation region made up of a bulksemiconductor material which has been doped to form a horizontalsemiconductor junction in the form of a p-n junction (although analternative semiconductor junction in the form of a horizontal p-i-njunction would be viable). The p-n junction is made up of a p-typeregion 331, 341 and an n-type region 332, 342. The p-type regions areeach graded into three layers of varying different doping strengths: p,p+ and p++ and the n-doped regions are also graded into three layers ofvarying doping strengths n, n+ and n++ arranged so that the p and nlayers overlap the arm waveguide and so that the p++ and n++ layers arefurthest away from the waveguide. Electrodes are located directly abovethe outward-most doped regions. In particular, the electrodes arelocated directly above the p++ and n++ layers of the doped regions.Suitable bulk semiconductor material for the modulation region includesSiGe or homogeneous silicon.

The graded p-n junction structure extends the size of the horizontaljunction and enables electrodes which apply a bias to the doped regionsto be placed advantageously away from the ridge. Each extra pair oflayers results in further spaced electrodes as the electrodes arepreferably located directly over the most heavily doped regions. Thisincrease in separation of the electrodes gives rise to an increasedflexibility of the device design without compromising speed.

Doping of a bulk semiconductor material to form an electro-opticalregion is known in the art, both in the case of modulators and alsodetectors. In all of the devices described herein, the dopingconcentrations used would correspond to typical values found in thestate of the art. For example, the doped regions of the detector mayinclude regions with concentrations of up to 10×10¹⁹ cm⁻³. Doped regionsof the modulator may take typical values of 10×10¹⁵ cm⁻³ to 10×10¹⁷ cm⁻³for p doped regions and 10×10¹⁵ cm⁻³ to 10×10¹⁸ cm⁻³ for n dopedregions. However, doped regions (p and/or n) may have higher values ofas much as 10×10²⁰ cm⁻³ or 10×10²¹ cm⁻³.

The additional phase shift region has a lower speed than the modulationregions so may be made of an alternative material such as homogeneoussilicon. In the embodiment shown, the additional phase shift regioncomprises a horizontal semiconductor junction in the form of a p-i-njunction, the p and n doped regions of which do not extend into thewaveguide of the first or second waveguide arm. In fact, the intrinsicregions 335, 345 extend beyond the boundary. Electrodes 339 a, 349 awhich apply a bias to the p-doped regions are located directly above therespective p-doped regions 333, 343 and electrodes 339 b, 349 b whichprovide a bias to the n-doped regions are located directly above then-doped regions 334, 344.

The electrodes above both the modulation regions and phase shift regionsare strips which lie along the length of the doped region (along adirection parallel to the longitudinal axis of the waveguide). It isdesirable for the electrodes to have as much contact with the respectivedoped regions as possible whilst also retaining the small sizes that areadvantageous to speed of modulation.

An input 1×2 coupler couples unmodulated light from the input waveguide9 into the two arms of the modulator and an output 2×1 coupler couplesthe light from the two arms into the output waveguide 6 to form amodulated output signal having the same wavelength as the unmodulatedinput signal. High-speed Mach-Zehnder modulators are known to the personskilled in the art and may take the form of the Mach-Zehnder modulatorsdescribed by Dong et al., Optics Express p. 6163-6169 (2012) or D. J.Thompson et al, Optics Express pp. 11507-11516 (2011). The phasedifference between modulated light exiting the first arm and modulatedlight exiting the second arm will affect the interference patterngenerated (in time) when light from the two arms combine, thereforealtering the amplitude of the light in the output.

Each arm includes a waveguide transition region 314, 324 between theinput 1×2 coupler and the phase shift region and another waveguidetransition region 315, 325 between the modulation regions and the output2×1 coupler. In this way, the waveguide dimensions within the resonatormodulator can be smaller than those of the input and output waveguides.This helps to improve the operation speed of the modulator (although itdoes so at the expense of higher losses).

A central electrical circuit 35 (which is an extension of the DRMelectrical circuit) is located between the modulation regions of one armand the modulation regions of the second arm. This circuit is requiredwhere the respective modulation regions of the two arms of the MZM aredriven in series in a single drive condition or in a dual drivecondition. The nature of this central electrical circuit 35 will controlboth whether the MZM is single drive or dual drive, but also whether thetwo arms are driven in series or in parallel.

The electrical circuit connection 34 between the M-Z modulator and thedetector (detector not shown) and the central circuit connection 35between modulation regions in the two arms can each take the form of anyone of the electrical circuit connections described above in relation toFIGS. 3a to 3d but is depicted in FIG. 5 as a stripline circuit in theform of a single metal strip with insulating filler material locatedunderneath the strip. In addition to this electrical connection, theMach-Zehnder modulator includes a further electrical connection 35located between a phase modulating region of the first arm 310 and acorresponding phase modulating region in the second arm 320 to connectan electrode 319 e over an n++ doped region of the phase modulatingregion 312 of the first arm 310 with an electrode 329 d over a p++ dopedregion of the corresponding phase modulating region 322 of the secondarm. A further alternative modulator is described below with referenceto in FIGS. 6, 7 and 8. This modulator can replace the EAM in theembodiment shown in FIG. 2 to form a further alternative DRM accordingto the present invention, where the remaining features and options ofthe DRM (other than the EAM) described in relation to FIG. 2 would stillapply. In this alternative DRM embodiment, the modulator is aFabry-Perot (F-P) resonator modulator 43.

The F-P resonator modulator 43 is formed in a single waveguide sectionby two reflectors in series with one or more modulation regions 411,412, 413 located between the two reflectors. In the embodiment shown inFIG. 6, the reflectors take the form of Distributed Bragg Reflectors(DBRs) DBR1, DBR2.

The Fabry-Perot resonator cavity shown in FIG. 6 actually includes aplurality of modulation regions 411, 412, 413 (3 of which are shown).These are formed in a bulk semiconductor medium and comprise a p-njunction the same as those of the modulation regions described above inrelation to FIG. 4.

Each modulation region 411, 412, 413 is made up of a bulk semiconductormaterial which has been doped to form a horizontal semiconductorjunction in the form of a p-n junction (although an alternativesemiconductor junction in the form of a horizontal p-i-n junction wouldalso be viable). Each p-n junction is made up of a p-type region 431 andan n-type region 432. The p-doped regions are each graded into threelayers of varying different doping strengths: p, p+ and p++; and then-doped regions are also graded into three layers of different dopingstrengths n, n+ and n++. These layers are arranged so that the p and nlayers overlap the waveguide, followed by the p+ and n+ layers and thep++ and n++ layers so that the p++ and n++ layers are furthest away fromthe waveguide. Electrodes are located directly above the outward-mostdoped regions. In particular, the electrodes are located directly abovethe p++ and n++ layers of the doped regions. Suitable material for themodulation region includes SiGe or homogeneous silicon.

The Fabry-Perot resonator cavity also includes an additional phase shiftregion 414 with a lower speed of operation than the modulation regions.As with the phase shift regions described above in relation to theMach-Zehnder modulator, the function of this phase shift region 414 isto provide low speed cavity FSR fine tuning and therefore operatingwavelength fine-tuning and thermal drift compensation. The phase shiftregion is shown in FIG. 6 as a p-i-n semiconductor junction operating ina carrier injection mode (but could alternatively comprise a p-n phaseshift region operating in a carrier depletion mode). As with the p-i-nphase shift regions described above, the p and n doped regions do notextend into the waveguide of the first or second waveguide arm. In fact,the intrinsic regions extend beyond the boundary. Electrodes 439 a whichapply a bias to the p-doped regions are located directly above therespective p-doped regions 433 and electrodes 439 b which provide a biasto the n-doped regions are located directly above the n-doped regions434.

The electrodes above both the modulation regions and phase shift regionsare strips located over the doped regions and lie along the length ofthe doped region (along a direction parallel to the longitudinal axis ofthe waveguide). The electrodes lie along the entire length of the dopedregions (length parallel to the longitudinal axis of the waveguide)because is desirable for the electrodes to have as much contact with therespective doped regions as possible whilst also retaining the smallsizes (small thicknesses) that are advantageous to speed of modulation.

An electrical circuit connection 44 between the F-P modulator and thedetector (detector not shown) can take the form of any one of theelectrical circuit connections described above in relation to FIGS. 3ato 3 d.

The F-P resonator is a resonant F-P filter (alsoinfinite-impulse-response, or IIR filters) which increases themodulation tuning efficiency at the expense of tuning speed, increasedtemperature sensitivity, and increase manufacturing complexity due tothe need for inclusion of the DBR gratings. In an IIR filter, the effectof the index change induced by the phase shifter is enhanced by thenumber of round-trips in the resonator cavity, thus a smaller injectedcurrent density (in the carrier injection case) or bias voltage (in thecarrier depletion case) is needed to perform modulation with the sameextinction ratio. Thus less optical or electrical amplification would beneeded to perform the modulation as compared to the EAM and M-Zembodiments previously described. However manufacturing complexity andtolerances are increased because to reach high modulation speeds of 25or 40 Gb/s, the photon lifetime of the cavity must be kept small (inaddition to the requirement to make a high-speed phase modulator)meaning the cavity length must be short and the Finesse sufficientlylow. Therefore the fabrication and design complexity is high due to theneed to incorporate DBR gratings with potentially short lengths and deepetch depths.

The F-P modulator includes a waveguide transition region 444 between theinput waveguide 9 and the first DBR and another waveguide transitionregion 445, between the second DBR and the output waveguide. At thefirst transition region 444, the waveguide height and width are reduced,and at the second transition region, the waveguide height and width areincreased. In this way, the waveguide dimensions within the cavity aresmaller than those of the input and output waveguides. This can be usedto help to improve the operation speed of the modulator (although itdoes so at the expense of higher losses).

Modulation of the resonator is described below in relation to FIGS. 7and 8. Referring to the reflectance spectra of FIG. 7, it is clear thatDBR gratings DBR1 and DBR2 are broadband reflectors which have equalreflectance over the operating bandwidth of the tunable laser. Thereflectance values R1 and R2 are chosen to give a Finesse value that islarge enough to create enough cavity round trips to enhance the effectof Δn (a sufficient X factor of the resonator) to sufficiently reducethe amount of drive current or voltage needed to perform the modulationwith the desired extinction ration, but small enough to give a cavitylifetime that is still <1/(bit period). The transmittance of theresonator preferably has a maximum value of between 0.8 and 1 and may be0.8 as shown in FIG. 7.

Referring to the transmittance spectra 92, 93 shown in FIG. 8, aresonant peak of the F-P cavity must be tuned to the wavelength of the(non-modulated) laser (P_(laser(λ))) in the on-state (FIG. 8a ).However, in the off-state (FIG. 8b ), the phase of the cavity is alteredto detune the resonance peak away from the wavelength of the laserthereby producing a sufficient modulation extinction ratio. When a biasis applied to the electrodes of the p-n junctions of the modulationregions, and the bias is modulated between the on and off states, thetransmittance spectrum is therefore switched between on and offpositions resulting in the output being modulated from on to off or viceversa. By actively adjusting the bias to the phase shift regions, thealignment of the resonant peak of the F-P cavity to the wavelength ofthe laser can be maintained in the presence of a thermal drift.

Further alternative modulators are described below with reference toFIGS. 9 to 13 b. Each of these modulators can replace the EAM in theembodiment shown in FIG. 2 to form a further alternative DRM accordingto the present invention where the remaining features and options of theDRM (other than the EAM) described in relation to FIG. 2 would stillapply. In each of these alternative embodiments, the modulator is a ringresonator modulator 53, 153.

Taking the first of two ring resonator DRM embodiments and referring inparticular to FIGS. 9 to 11, the ring resonator modulator 53 is formedfrom a ring waveguide section, a first straight waveguide 59 coupled atone side of the ring waveguide and a second straight waveguide 60coupled to the other side of the ring waveguide. The ring waveguide isdefined between an inner waveguide ridge edge 56 and an outer waveguideridge edge 57. The cross section across dashed line M-N in FIG. 9 isshown in FIG. 10. The ring resonator modulator also comprises a ofmodulation region 512 formed in a bulk semiconductor medium doped togive a circular p-n junction which is set horizontally across thewaveguide (An alternative semiconductor junction in the form of ahorizontal p-i-n junction would also work).

Throughout this document, ring waveguides may take the form of any ringshape including: a circle (as shown in FIGS. 9 and 12), a race track; oran elliptical shape. Furthermore, the circular doped regions may takethe form of a circle with constant radius; a race-track shape; or anelliptical shape.

In the embodiment shown in FIG. 9, the circular p-n junction becomesdiscontinuous along a portion of its circumference where a continuouscircular doped region would otherwise overlap with the input and outputstraight waveguides. Suitable bulk semiconductor materials for themodulation region include SiGe and homogeneous silicon.

The p-n junction is made up of a p-type region 551 and an n-type region552. The p-doped regions are each graded into three concentric layers ofvarying different doping strengths: p, p+ and p++ and the n-dopedregions are also graded into three concentric layers of varying dopingstrengths n, n+ and n++ arranged so that the p and n layers overlap thering waveguide and extend radially outwards and inwards respectivelywithin the horizontal plane of the junction beyond the outer and innerwaveguide ridge edges. The p++ and n++ doped layers lie furthest awayfrom the ring waveguide. Because of the discontinuous nature of theouter doped portions, the p+, p++, n+ and n++ layers are each made up oftwo opposing crescent shaped regions rather than complete circular shapeas they do not extend the full way around the ring waveguide. This givesclearance for the straight waveguides 59, 60 which couple light in andout of the ring waveguide thereby ensuring that the p-n junction doesnot modify the refractive index in the light-coupling regions, andtherefore does not modify the coupling ratio between the ring and thestraight waveguides.

A ring gap separation 55 exists on either side of the ring waveguidebetween the ring waveguide and each of the straight waveguides 59, 60.The magnitude of this gap determines the value of the couplingcoefficient κ of the resonator.

Electrodes are located directly above the outer-most and inner-mostrespective doped regions. In particular, the electrodes are locateddirectly above the p++ and n++ layers of the doped regions. A centralcircular electrode 439 b is located above the n++ doped region to applya bias to the n-doped region. A bias is applied to the p-doped regionvia a looped electrode 439 a which extends above and along the crescentshaped p++ regions forming two crescent shaped electrode portions whichare then joined together by further electrode portions crossing over oneof the straight waveguides to form a closed single electrode.

An electrical circuit connection 54 between the ring resonator modulatorand the detector (detector not shown) can take the form of any one ofthe electrical circuit connections described above in relation to FIGS.3a to 3 d.

The ring resonator modulator 53 includes a first waveguide transitionregion 544 between the modulator input waveguide 9 and the firststraight waveguide 59 which couples light into the ring resonator and asecond transition region 545 between the second straight waveguide whichcouples light out of the waveguide and the modulator output waveguide 6.

At the first transition region 544, the waveguide height and/or widthare reduced, and at the second transition region, the waveguide heightand/or width are increased. In this way, the waveguide dimensions withinthe ring resonator modulator are smaller than those of the input andoutput waveguides. This helps to improve the operation speed of themodulator (although it does so at the expense of higher losses).

The transmittance spectrum of the ring resonator is shown in FIG. 11 asa periodic set of peaks, each peak separated from the adjacent two peaksvia a wavelength difference equal to the free spectral range (FSR) ofthe ring resonator. The free spectral range of the transmittance signalbeing set by the size of the ring waveguide. The transmittance of theresonator preferably has a maximum value of between 0.8 and 1 and may be0.8.

Modulation of the light occurs via the same process as the F-Pmodulator, the ring resonance must be tuned to the wavelength of the(non-modulated) laser (P_(laser(λ))) in the on-state (FIG. 8a ).However, in the off-state (FIG. 8b ), the phase of the cavity is alteredto detune the resonance peak away from the wavelength of the laserthereby producing a sufficient modulation extinction ratio. When a biasis applied to the electrodes of the p-n junctions of the ring, and thebias is modulated between the on and off states, the transmittancespectrum is therefore switched between on and off positions resulting inthe output being modulated from on to off or vice versa.

The ring resonator modulator 53 also includes a fine tuning region inthe form of a heater (not shown) for thermal tuning.

By actively adjusting the voltage across the phase tuning heater pads 58a and 58 b, the alignment of the resonant peak of the F-P cavity to thewavelength of the laser can be maintained in the presence of ambientthermal drift.

Referring to FIGS. 10, 12, 13 a, and 13 b, the ring resonator modulator153 according to the second of the two ring resonator DRM embodiments isdescribed. The difference between the ring resonator modulator of FIG.12 and that of FIG. 9 is the fact that the ring waveguide of theresonator modulator of FIG. 12 is coupled to no more than one straightwaveguide. A single straight waveguide 159 only is coupled to the ringwaveguide at one side. In this embodiment, the single straight waveguideis therefore configured to couple light both into and out of the ringwaveguide.

As with the previous ring resonator embodiment, the ring waveguide isdefined between an inner waveguide ridge 56 and an outer waveguide ridge57. The cross section across dashed line M-N for this embodiment is alsoshown by FIG. 10 and the parts of the description above relating to FIG.10 therefore apply here. In particular, the ring resonator embodiment ofFIG. 12 also includes a modulation region 512 formed in a bulksemiconductor medium doped to give a circular p-n junction which is setalong a horizontally across the waveguide.

The p-n junction is made up of a p-type region 551 and an n-type region552. The p-doped regions are each graded into three concentric layers ofvarying different doping strengths: p, p+ and p++ and the n-dopedregions are also graded into three concentric layers of varying dopingstrengths n, n+ and n++ arranged so that the p and n layers overlap thering waveguide and extend radially outwards and inwards respectivelybeyond the waveguide ridge edges 56, 57 within the horizontal plane ofthe semiconductor junction.

The p, n, n+ and n++ regions are ring shaped. However the p+ and p++regions on the outside of the p-type region are C-shaped; defining adiscontinuity where the ring waveguide comes into close contact with thestraight waveguide (i.e. where the outer-most doped regions wouldotherwise overlap the straight waveguide). The clearance between thedoped regions and the straight waveguide ensures that the p-n junctiondoes not modify the refractive index in the light-coupling regions, andtherefore does not modify the coupling ratio between the ring and thestraight waveguide.

A ring gap separation 155 exists between the ring waveguide and thesingle straight waveguide 159, the magnitude of which determines thevalue of the coupling coefficient κ of the resonator.

Electrodes are located directly above the respective outer-most andinner-most doped regions that they apply a bias to. In particular, theelectrodes are located directly above the p++ and n++ layers of thedoped regions. A central circular electrode 439 b is located above then++ doped region to apply a bias to the n-doped region. A bias isapplied to the p-doped region via a looped electrode 439 a which extendsalong the C-shaped (i.e. the full length of the discontinuouscircumference of the p++ region).

An electrical circuit connection 54 between the ring resonator modulatorand the detector (detector not shown) can take the form of any one ofthe electrical circuit connections described above in relation to FIGS.3a to 3 d.

The ring resonator modulator 153 includes a first waveguide transitionregion 544 between the modulator input waveguide 9 and the singlestraight waveguide 59 which couples light into the ring resonator and asecond transition region 546 between the single straight waveguide 59and the modulator output waveguide 6.

At the first transition region 544, the waveguide height and width arereduced, and at the second transition region, 546 the waveguide heightand width are increased. In this way, the waveguide dimensions withinthe ring resonator modulator are smaller than those of the input andoutput waveguides.

The transmittance spectrum of the ring resonator is shown in FIGS. 13aand 13b , and takes the form of a periodic set of sharp troughs, eachtrough separated from the two directly adjacent troughs via a wavelengthdifference equal to the free spectral range (FSR) of the ring resonator.As this transmittance spectrum is the inverse of that for the “dualstraight waveguide” embodiment, the ring resonator modulator of FIGS.12, 13 a, and 13 b will require an opposite drive signal (bias appliedacross the p-n junction) as compared to the single coupled waveguideversion in order to give rise to the same modulation effect.

The transmittance of the resonator in the troughs preferably has amaximum value of between 0.8 and 1, and may be 0.8. As with the previousring resonator embodiment, modulation is achieved when a bias is appliedacross the p-n junctions from the electrical circuit connector via theelectrodes. This tunes the transmittance spectrum on and off resonancewith the wavelength of the (unmodulated) laser which in turn results inthe transmitted output signal being turned on 94 and off 95. However,because the transmittance is a trough on resonance, the magnitude ofbias change is larger to get the same extinction ratio for the “dualstraight waveguide” embodiment.

An advantage of this embodiment is that there is only one straightwaveguide and one discontinuous portion in the p-n junctions around thecircumference, meaning the electrode for the p-doped region does nothave to cross over a straight waveguide. When metal electrodes cross awaveguide additional optical loss is introduced.

The ring resonator modulator 153 also includes a fine tuning region inthe form of a heater (not shown) for thermal tuning. By activelyadjusting the voltage across the phase tuning heater pads 58 a and 58 b,the alignment of the resonant peak of the F-P cavity to the wavelengthof the laser can be maintained in the presence of ambient thermal drift.

An example of a traditional data center interconnection network is shownin FIG. 14. Switching between top of rack (ToR) switch units is achievedusing: access switches, aggregation routers and core routers. In the(simplified) example shown in FIG. 14, many cables are needed to switchbetween 4 ToR switch units. The top of rack (ToR) switch is an exampleof a device in a network, typically in or connected to a server, whichmay supply signals to and receive signals from the optoelectronicswitches of this invention (such that the ToR forms an element at theendpoint of an electrical signal coming from a server). However, infact, any of the optoelectronic switches described herein could beapplied to a system with no ToR switches, for example by switchingdirectly between servers in a datacenter (or any other electronics baseddevices).

An example of a network including an optoelectronic switch is shown inFIG. 15. The access and aggregation packet switches of traditionalarchitecture are replaced by a single optoelectronic switch. In the(simplified) example shown in FIG. 15, many fewer cables are needed toswitch between 4 ToR switch units. The number of transceivers requiredis therefore also substantially reduced. It would be clear to theskilled person that whilst the optoelectronic switches described hereinare capable of use as part of an network as shown in FIG. 15, they couldalso be used to switch optical signals in other network configurationsand other uses, particularly uses in networks where switches areconnected with optical interconnects, or for which high speed, lowpower-consumption, and high radix switching is important.

Examples of optoelectronic switches and DRMs according to the presentinvention are described below with reference to FIGS. 16a to 29.

An optical chip 160 a which forms a portion of an optoelectronic switchis shown in FIG. 16a . The chip includes a plurality of DRMs (DRM1,DRM2, DRM3, DRM4), each configured to receive an optical input signal161 a, 162 a, 163 a, 164 a from one or more switch inputs. Where theoptoelectronic switch is an optoelectronic packet switch, these inputswill be optical packet signals. Where the optoelectronic switch is anoptoelectronic circuit switch, the optical input signals will not needto include packet header information.

Each DRM includes one or more detectors (not shown) and one or moremodulators (not shown) in detector/modulator pairs (i.e. the number ofmodulators is equal to the number of detectors). Any of the detectorsand/or modulators may take the form of any one of the detectors and/ormodulators described above in relation to FIGS. 1 to 14. Each detectorreceives an optical input signal and generates an electrical signalcontaining the information of that optical input signal. Where theoptical input signal is a packet signal, the electrical signal generatedwill be an electrical packet signal.

Each of the one or more modulators of a DRM is configured to receive awavelength tuned laser light input 165, 166, 167, 168 from a respectivetunable laser (TL1, TL2, TL3, TL4) and to receive the respectiveelectrical signals from the one or more respective detectors. Thewavelength tuned light from the tunable laser is modulated by themodulator according to the information contained in the electricalsignal to generate a modulated output signal 1601, 1602, 1603, 1604containing that information but at the desired wavelength for switching.

In FIG. 16a , the DRMs and tunable lasers are arranged such that opticalinput signals 161 a, 162 a, 163 a, 164 a impinge the modulator at anangle to the plane of the chip (and therefore at an angle to the planeof the passive optical router such as an AWG (not shown in this figure).

The chip 160 a may be a silicon-on-insulator chip and may be a singleintegrated chip or made up of two or more components abutted next to oneanother. For example, separate chips may join at an abutment surface169, the array of tunable lasers (TL1-TL4) being located on a separatechip to the DRMs (DRM1-DRM4) to prevent undesirable heating of the DRMsby the tunable lasers.

The optical chip of FIG. 16b differs from that of FIG. 16a in that theoptical signal inputs are provided by way of signal input waveguide viawhich lie within the plane of the DRMs and the passive optical router(such as an AWG, not shown).

In the arrangements depicted in FIGS. 16a and 16b the plurality oftunable lasers (TL1-TL4) are arranged in a first linear array, and theplurality of DRMs are arranged in a second linear array parallel to thefirst array, although other geometric arrangements are envisaged. Inaddition, although 4 DRMs are shown, more or fewer DRMs could bepresent.

In FIG. 17, two optoelectronic chips 160 b-1, 160 b-2 such as that shownin FIG. 16a are shown aligned with a third chip which comprises apassive optical router in the form of an AWG. The AWG is arranged alongthe same plane as the tunable lasers, the DRMs and the waveguidesinterconnecting the various components. The AWG itself comprises aninput coupler 172 and an output coupler 173 connected via a plurality ofpaths defined by a plurality of waveguides. A first plurality of DRMs(DRM1-DRM4) are located at the input of the passive optical router, anda second plurality of DRMs (DRM5-DRM8) are located at the exit of thepassive optical router.

The AWGs described throughout this application may be made in siliconand if so may be fabricated on the same chip as the DRMs and tunablelasers. If the AWG is made of another suitable material such as silicaon silicon or polymer it may be butt coupled to the silicon-on-insulatorchip such that it lies in the same plane as the DRMs and tunable lasers.

Modulated optical signals which exit the first plurality of DRMs arecoupled to the input coupler 172 of the AWG. The path taken by amodulated optical signal through the AWG to the output coupler 173 (andtherefore the port from which the modulated optical signal leaves theAWG) will depend on its wavelength.

The second plurality of DRMs (DRM5-DRM8) form an array located after theoutput coupler of the AWG, each DRM positioned to receive a modulatedoptical signal from a specific output port of the AWG. Each of the DRMsin the second DRM array operates via the mechanism described about inrelation to the first DRM array, the modulator of each being configuredto receive wavelength tuned light from a respective tunable laser(TL5-TL8) and an optical signal from each respective AWG output port toproduce a modulated optical signal of the desired tuned wavelength.

The passive optical router of any one of the embodiments describedherein may take the form of a plurality of passive optical routersconnected in a parallel arrangement as shown in FIGS. 18a, 18b and 18 c.

In FIG. 18a is shown an arrangement in which four AWGs (AWGs 1-4) areconnected in a planar arrangement with sixteen input DRMs (DRMs 1-16)and 16 output DRMs (DRMs 17-32). Here the input and output DRMs arearranged in groups of 4 DRMs, each group being lit with a single lasercoupled with a series of 1×2 couplers in waveguides. The couplers may bestar couplers. Thus each group of four DRMs is operated at the sametunable wavelength. Each of the outputs of each in the series of 4 DRMsis coupled to a different one of the 4 AWGs. This arrangement is usefulin, for example, switching a channelized packet signal. For example,four 25G lanes of data may be processed from a source of 100G data inthe PSM4 MSA standard. In this example the four lanes of data followparallel routes through the switch. The AWGs and the DRMs and the lasersmay be fabricated on the same chip, for example an SOI chip, or theco-planar arrangement may be achieved by butt coupling of separate chipsor devices to achieve the illustrated coplanar arrangement. The line ABshown in FIG. 18a shows a possible location for the butt coupling of twochips. In FIG. 18a the DRMs 5-8, 9-12, 21-24 and 25-29 have been omittedfor reason of the clarity of presentation. The connectivity of DRMs toAWG input output waveguides is denoted as D1-D32 with the connectivityof one AWG only indicated on FIG. 18a . It will be noted that FIG. 18ais schematic and, for the sake of clarity, shows waveguide bends andcrossings of impractical shapes and relative dimensions. One skilled inthe art would be able to design a working device from the FIG. 18a andthe description here provided.

Alternative embodiments with the same overall topology are shown inFIGS. 18b and 18c . In FIG. 18b , the AWGs are stacked one above theother in an appropriate optical package. The DRMs are fabricated onseparate chips and the tunable lasers are fabricated on separate chipsin arrays. In this example there are 4 tunable lasers (TLs 1-4) on asingle chip 1801, each tunable laser is arranged to produce 4 outputlights. This is achieved by a series of 1×2 couplers in waveguides. Fourinput fibers (I) are shown connected to the input waveguides of the DRMs(DRMs 1-IN). There are fiber connections (e.g. a fiber ribbon) from thetunable laser chip to the DRM chips such that a chip with four DRMsreceives 4 laser inputs of the same wavelength and each of the outputsof the 4 DRMs are connected by fiber to a different AWG (AWGs 1-4). Theoutputs of the AWGs are arranged so that the 4 outputs of a givenwavelength are directed by fiber to a set of 4 DRMs and are output fromthe device in a group of 4 fibers (O). Shown in FIG. 18b are DRMs 17-20OUT. The source of laser light (TL source) for the DRMs 17-32 is notshown. Laser sources could be arranged in arrays on chips in like mannerto the tunable lasers 1-4. In FIG. 18c , the tunable lasers and DRMs arearranged on the same chip. For clarity, the DRMs 5-16 and 21-32 and thetunable lasers 2-4 and 6-8 are not shown. In order to avoid waveguidecrossings, the DRM chips of this embodiment are laid out so that thelaser inputs enter on the same side of the chip as the outputwaveguides. Again each of the 4 DRMs on the chip is lit with laser lightof the same wavelength from a single laser coupled to the DRMs viawaveguides and a series of 1×2 couplers.

The embodiments of FIGS. 18a, 18b and 18c are exemplary and otherarrangements including other chip layouts will be apparent.

For simplicity each of the passive optical routers shown below aresingle passive optical routers or a first passive optical routerarranged in series with a second passive optical router. It is envisagedthat any one of the passive optical routers below could take the form ofa plurality of parallel passive optical routers as described above.

As already described in relation to FIG. 18a , the DRMs and the passiveoptical router may be integrated on a single chip. Such an arrangementis shown in FIG. 19, in which a single integrated chip 190 (e.g.silicon-on-insulator) includes in a planar arrangement: a passiveoptical router 191 in the form of an AWG, a plurality of DRMs (DRM1,DRM2, DRM3, DRM4) and a plurality of tunable lasers (TL1, TL2, TL3,TL4). As with the previous embodiments described above, each of the DRMsis configured such that the modulator (not shown) receives wavelengthtuned light from a respective tunable laser and such that the detector(not shown) receives an optical input signal from a respective one of aplurality of inputs (IN1, IN2, IN3, IN4), each of which are opticallyconnected to a respective input via a waveguide. In the embodiment shownin FIG. 19, each DRM output is connected to an input port of the inputcoupler 193 of the AWG and each output port of the output coupler 194 ofthe AWG is connected to a respective output of the chip (OUT1, OUT2,OUT3, OUT4).

In the embodiment shown, the inputs and outputs are located at oppositesides of the chip.

FIG. 20 shows another optoelectronic switch. This switch contains theoptical components described above in relation to FIG. 17 but differsfrom the embodiment of FIG. 17 in that the optoelectronic switch is asingle integrated chip 200 (e.g. a silicon-on-insulator chip).

In the embodiment shown, the inputs and outputs are located on the sameside of the chip as one another.

An optoelectronic switch 2120 with a single input 2103 and single output2104 is shown in FIG. 21. The optoelectronic switch is made up of aswitch corresponding to the optoelectronic switch 170 shown in FIG. 17with an additional demultiplexer chip 2101 and multiplexer chip 2102.Each of the multiplexer and demultiplexer may take the form of anadditional AWG (or alternative passive optical router such as an Echellegrating), and each are positioned in a planar arrangement with the AWG.

One or both of the multiplexer and demultiplexer could equally beapplied to any of the other optoelectronic switches described hereinwhich have multiple inputs and/or multiple outputs. The multiplexer anddemultiplexer could be Echelle gratings.

In FIG. 21, the optoelectronic switch takes the form of multiple chipsabutted against one another. In an alternative embodiment it isenvisaged that the components shown could be integrated onto a singleoptical chip. Either way, the chip/chips may be silicon-on-insulatorchip(s). The AWG (or other passive optical router such as an Echellegrating) may be made from a suitable material other than silicon.

Switch functionality and/or capacity may be increased by adding one ormore extra passive optical routers in series with the first opticalrouter.

FIGS. 22 to 24 depict embodiments of optoelectronic switches containingtwo passive optical routers. DRMs are located at the inputs of the firstAWG to generate a modulated optical signal with the desired wavelength(corresponding to the output port required). Upon exiting the first AWGit may again be necessary to change the wavelength of the output signalin order to further propagate the signal through the second AWG to thedesired exit port.

In the embodiment of the optoelectronic switch 2200 of FIG. 22 a firstAWG (AWG1) and a second AWG (AWG2) are successive elongated arcspositioned on an integrated chip in an end-to-end configuration along anelongated optical chip 2201.

In the embodiment of the optoelectronic switch 2300 shown in FIG. 23 thefirst AWG (AWG 1) and a second AWG (AWG 2) are positioned in a nestedconfiguration such that the arched waveguides of the first AWG arch inthe same direction as those of the second AWG (AWG2). In the embodimentshown in FIG. 22, the first AWG and second AWG are the same size as oneanother. However, it is envisaged that in a different embodiment thefirst AWG may be smaller than the second AWG or vice versa.

In the embodiment of the optoelectronic switch 2400 shown in FIG. 24 thefirst AWG (AWG 1) and a second AWG (AWG 2) are positioned in an S-shapedconfiguration such that the arched waveguides of the first AWG arch inthe opposite direction to those of the second AWG (AWG2).

In all of the embodiments shown in FIGS. 22 to 24 the optoelectronicswitch is formed on a single integrated chip (e.g. asilicon-on-insulator chip). However, it is envisaged that separate chipscould be used for specific components (such as the tunable laserarrays).

A schematic diagram of a DRM for an optoelectronic packet switch isshown in FIG. 25. The DRM 2500 comprises: a detector 2501; a modulator2502; and an electronic circuit 2503 which forms an electricalconnection between the detector and the modulator via a number ofadditional components. A tunable laser 2504 is located outside of theelectrical circuit as a separate component from the modulator 2502 andprovides the modulator with a wavelength tuned but unmodulated lasersignal.

The electronic circuit includes laser wavelength tuner module 2511configured to send tuning signals to the tunable laser. The tunablelaser is configured to generate a wavelength tuned (but unmodulated)laser light signal which acts as an optical input for the modulator2502, the wavelength of which is selected by the laser wavelength tunermodule 2511 of the electronic circuit. The module 2511 which includesthe wavelength tuner may include a laser driver as shown in FIG. 25although it is also envisaged that the laser driver could be locatedoutside of the electronic circuit (not shown).

The electronic circuit 2503 receives an electrical input from thedetector 2501 which is first amplified by an amplification unit 2505which may take the form of a transimpedance amplifier (TIA) and acts toprovide gain to the electrical packet signal generated by the detector,and conversion from current to voltage.

Once gain has been provided, the electrical signal is decoded by aPhysical Coding Sublayer (PCS) and a Physical Medium Attachment (PMA)which is responsible for the serialisation of the incoming data. 2506.The PMA effectively regenerates the signal.

The output of the PCS/PMA 2506 is connected to the input of a framer2507 which identifies the frames in the signal. The first copy of theframe is sent to a packet processor 2508 which determines the desiredoutput port for the packet and sends this information to the externalswitch control unit 2510.

The switch control unit includes a scheduler (not shown) whichconstructs a schedule of how packets are to traverse the passive opticalrouter. The scheduler sends this schedule to a finite state machine(FSM) 2509. Based on the schedule, the FSM generates control signalswhich instruct the laser wavelength tuner 2511 to set the appropriatewavelength of the tunable laser 2504. The appropriate wavelength is thewavelength required for the path of the modulated optical signal throughthe passive optical router to exit the passive optical router at adesired output port. The schedule sent to the FSM from the schedulerwill take into account the paths of other packets through the passiveoptical router at the same time.

The second copy of the frame which has been generated by the framer 2506is sent to an SRAM packet queue 2512, where the frame is buffered untila control signal from the FSM 2509 indicates that the frame is to betransmitted. The addition of buffers allows higher throughput (bits orbytes per second) through the switch by solving the problem of allowingpackets destined to the same output port to be delayed until the outputport is no longer in use.

Once transmitted from the SRAM packet queue 2512, the frame is sent to asecond framer 2513, recoded into the desired format and serialized at asecond PCS/PMA 2514 and then sent to the modulator 2502 via modulatordriver 2516.

An alternative DRM 2600 is shown in FIG. 26 where like reference numberscorrespond to those features described above in relation to FIG. 25. Theembodiment in FIG. 26 differs from that of FIG. 25 in that the packetprocessor is located within the switch control unit and thereforeoutside of the electronic circuit 2603. In this embodiment, a copy ofthe frame is sent directly to the switch control unit 2610 from thefirst framer 2607 so that header processing of the packet and schedulingboth take place within the switch control unit, i.e. outside of the DRM.

A further example of a DRM, in this case suitable for use in anoptoelectronic circuit switch, is shown in FIG. 27. Like referencenumbers correspond to those features described above in relation toFIGS. 25 and 26.

The DRM 2700 comprises: a detector 2701, a modulator 2702, and anelectronic circuit 2703 which forms an electrical connection between thedetector and the modulator via only mainly analogue/mixed signalcircuitry without going into the digital domain. A tunable laser 2704 islocated outside of the electronic circuit as a separate component fromthe modulator 2702 and provides the modulator with a wavelength tunedbut unmodulated laser signal.

The electronic circuit includes laser wavelength tuner module 2711configured to send tuning signals to the tunable laser. The tunablelaser is configured to generate a wavelength tuned (but unmodulated)laser light signal which acts as an optical input for the modulator2702, the wavelength of which is selected by the laser wavelength tunermodule 2711 of the electronic circuit. The module 2711 which includesthe wavelength tuner may include a laser driver as shown in FIG. 25although it is also envisaged that the laser driver could be locatedoutside of the electrical circuit (not shown).

The electronic circuit 2703 receives an electrical input from thedetector 2701, and the electrical input is first amplified by anamplification unit 2705 which may take the form of a transimpedanceamplifier (TIA) and acts to provide gain to the electrical packet signalgenerated by the detector, and conversion from current to voltage.

Once gain and voltage conversion has been provided, the electricalsignal is then optionally sent to a regenerator 2706 which providesadditional reshaping and retiming to the signal, and prepares the signalto have sufficient magnitude and quality to input to the modulatordriver and generate an optical signal of desired quality.

The switch control unit 2710 directly controls the modulator driver andthe wavelength tuner module using external inputs.

The signal is then sent to the modulator 2702 via modulator driver 2716.

The electronic circuits described above in relation to FIGS. 25 to 27could form the electrical circuit of any one of the embodimentsdescribed in relation to FIGS. 1 to 13 b. Thus the modulator and/or thedetector of FIGS. 25 to 27 may take the form of any one of the detectorsand/or modulators described in more detail in FIGS. 1 to 13 b of thisapplication. Furthermore, although the electronic circuit in FIGS. 25 to27 connect a single detector to a single modulator, it is envisaged thatthe circuit could be scaled up to connect one or more detectors with oneor more modulators.

An embodiment of an optoelectronic switch 2800 is shown in FIG. 28. Theoptoelectronic switch could be an optoelectronic packet switch or anoptoelectronic circuit switch.

An interface of the optoelectronic switch 2800 includes a plurality ofswitch input ports for receiving optical signals to be switched using apassive optical router 2801 and a plurality of switch output ports fortransmitting optical signals received from the passive optical router.In the embodiment shown, the passive optical router takes the form of anAWG although it is envisaged that other passive optical routers could beused.

Each switch input port 2804 is connected to a specific DRM 2802 via anoptical fiber 2803. In fact a plurality of input ports are connected toeach DRM by a plurality of respective optical fibers. Each fiberconnects a specific switch input to a specific one of a plurality ofdetectors within the DRM. The optoelectronic switch is configured tosplit an inputted packet into a plurality of paths/lines and to processthe plurality of lines of data in parallel, each channel having its owndetector, its own modulator and its own output fiber.

For each input port 2804, the detector will receive an optical signalfrom its respective input and will convert this into an electricalsignal (if the optoelectronic switch is an optoelectronic packet switch,the electrical signal generated by the detector will be an electricalpacket signal).

The electrical signal will be processed by the DRM as described inrelation to FIG. 25, 26 or 27 based on scheduling information (in thecase of an optoelectronic packet switch) or other control information(in the case of an optoelectronic circuit switch). Based on thisinformation, the electrical signal will be sent to one or moremodulators.

Each modulator is configured to receive a modulated electrical signalfrom one or more channels within the electrical circuit and also toreceive a wavelength tuned laser input. In the embodiment shown in FIG.28, the tunable lasers are located on the switch control unit 2806.

A DRM bus 2807 forms a bidirectional connection between the switchcontrol unit and each of the DRMs for communication of information toand from the switch control unit.

A further optical fiber 2808 in the form of a 4 line ribbon fiberconnects the outputs port of each DRM to an input port of the passiveoptical router.

In order to further decrease the time taken for a single packet to beswitches, data packets which enter each input port 2804 of theoptoelectronic switch (and therefore each packet which passes through aDRM) is separated into a plurality of lanes which are processed inparallel.

In the embodiment shown, there are a total of 6 DRMs arranged in alinear array, each of which is configured to receive inputs from 4 inputports. Each channel between an input port and a DRM is then itself splitinto 4 lanes which are processed in parallel.

An alternative arrangement of an optoelectronic switch 2900 is shown inFIG. 29 connected to two top of rack switches 2904 a, 2904 b betweenwhich data is to be switched. A plurality of DRMs 2902 are located as anarray, each DRM at an input of a passive optical router (in the form ofan AWG 2901) to provide optical modulated signals to the input ports ofthe AWG. As with previous embodiments, the DRMs are either located onthe same chip as the AWG of on adjacent abutting chips which areoptically connected to the chip of the AWG.

An array of tunable lasers 2903 is located separately from the AWG andDRMs, and each tunable laser is optically connected to the input of oneof the DRMs via a wavelength agnostic optical fibre.

The first ToR from which data is to be switched is connected to themodulator of one of the plurality of DRMs 2902. The DRM receives opticalinput signals of undefined wavelengths and routes them through thepassive optical router (in this case an AWG) by modulating the tunedlaser signal from one of the tunable lasers, the wavelength of thetunable laser chosen to select a specific path through the passiveoptical router to a particular output port of the passive opticalrouter.

This arrangement has the advantage that the more expensive opticalequipment is kept separate from the parts of the switch required tocarry the signal from and to the ToR. One or more of the tunable lasersmay take the form of a Vertical Cavity Surface-Emitting Laser (VCSEL) oranother suitable laser which is driven by direct modulation.

While the invention has been described in conjunction with the exemplaryembodiments described above, many equivalent modifications andvariations will be apparent to those skilled in the art when given thisdisclosure. Accordingly, the exemplary embodiments of the invention setforth above are considered to be illustrative and not limiting. Variouschanges to the described embodiments may be made without departing fromthe spirit and scope of the invention.

For example, the detectors such as photodetectors of any one of theembodiments above could be replaced with other types of receiverssuitable for receiving optical or electrical signals.

All references referred to above are hereby incorporated by reference.

The invention claimed is:
 1. A silicon-on-insulator chip comprising: afirst arrayed waveguide grating (AWG) comprising a plurality ofwaveguides in a plane, one or more inputs, and one or more outputs; anda first array of detector remodulators (DRMs), each of the DRMscomprising: a detector; a modulator; and a CMOS circuit connected incascade between the detector and the modulator, the detector beingconfigured to convert an input modulated optical signal to an electricalsignal and comprising a first semiconductor junction arranged in theplane and the modulator being configured to modulate an output opticalsignal using the electrical signal and comprising a modulation waveguideregion at which a second semiconductor junction is set horizontallyacross the modulation waveguide region in that the second semiconductorjunction comprises a first doped region of the modulation waveguideregion and a second doped region of the modulation waveguide regionwhich is on an opposite side of the modulation waveguide region to thefirst doped region in a horizontal direction; the first array of DRMsbeing in a planar arrangement with the first AWG such that themodulators of the DRMs are located within the plane; and wherein eachDRM is located at an input or output of the AWG, wherein an inputwaveguide for the input modulated optical signal for one or more of theDRMs lies within the plane.
 2. The silicon-on-insulator chip of claim 1,wherein the detectors of the DRMs are located within the plane.
 3. Thesilicon-on-insulator chip of claim 1, wherein a respective DRM of thefirst array of DRMs is located at each of one or more inputs of thefirst AWG and at each of one or more outputs of the first AWG.
 4. Thesilicon-on-insulator chip of claim 3, wherein a respective DRM of thefirst array of DRMs is located at each input of the first AWG and ateach output of the first AWG.
 5. The silicon-on-insulator chip of claim3, wherein a signal input waveguide for one or more of the DRMs lieswithin the plane.
 6. The silicon-on-insulator chip of claim 3, wherein asignal input waveguide for one or more of the DRMs impinges themodulator of the DRM from an angle to the plane.
 7. A system comprising:the silicon-on-insulator chip of claim 1; and one or more tunablelasers, each tunable laser being for providing a wavelength tuned laserinput to the modulator of a respective one or more of the DRMs.
 8. Thesystem of claim 7, wherein the one or more tunable lasers are located onthe silicon-on-insulator chip.
 9. The system of claim 8, wherein the oneor more tunable lasers are located within the plane.
 10. The system ofclaim 7, wherein a tunable laser of the one or more tunable lasers isthermally isolated from the first AWG and the DRMs.
 11. The system ofclaim 7, wherein the one or more tunable lasers lies within the plane.12. The system of claim 7, wherein: a respective DRM of the first arrayof DRMs; and a respective tunable laser, of the one or more tunablelasers, are located at each input of the first AWG, the tunable laserbeing configured to provide the wavelength tuned laser input for themodulator of the DRM.
 13. The system of claim 7, wherein: a respectiveDRM of the first array of DRMs; and a respective tunable laser, of theone or more tunable lasers, are located at each output of the first AWG,the tunable laser being configured to provide the wavelength tuned laserinput for the modulator of the DRM.
 14. The silicon-on-insulator chip ofclaim 1, wherein: the first AWG has a plurality of inputs and aplurality of outputs; each of the first array of DRMs being located at arespective input of the first AWG, each DRM of the first array of DRMsbeing configured to receive a wavelength tunable laser input; the firstarray of DRMs being arranged such that an output of each DRM of thefirst array of DRMs is configured to form an input signal for the firstAWG; the silicon-on-insulator chip further comprising: a second AWGhaving a plurality of inputs and a plurality of outputs; and a secondarray of DRMs, each located at a respective input to the second AWG;each DRM of the second array of DRMs being configured to receive awavelength tunable laser input; the second array of DRMs being arrangedsuch that an output of each DRM of the second array of DRMs isconfigured to form an input signal for the second AWG; wherein eachoutput of the first AWG is configured to form an input signal for arespective DRM of the second array of DRMs, and wherein: the DRMs of thefirst array of DRMs, the second AWG, and the DRMs of the second array ofDRMs are in the plane.
 15. The silicon-on-insulator chip of claim 14,wherein the first and second AWGs are located in an end-to-endarrangement on the silicon-on-insulator chip.
 16. Thesilicon-on-insulator chip of claim 15, wherein the first and second AWGsare positioned in a nested arrangement within the plane.
 17. Thesilicon-on-insulator chip of claim 1, wherein: each DRM of the firstarray of DRMs is located at an input waveguide of the first AWG, andeach DRM of the first array of DRMs is coupled to a tunable laser whichis configured to provide a wavelength tuned input for the modulator ofthe DRM; the silicon-on-insulator chip further comprising: a secondarray of DRMs; each DRM of the second array of DRMs being located at anoutput waveguide of the first AWG and each DRM of the second array ofDRMs being coupled to a tunable laser which is configured to provide awavelength tuned input for the modulator of the DRM; an opticaldemultiplexer, an output of which is configured to form input signalsfor the first array of DRMs; and an optical multiplexer, the inputs forwhich are the outputs of the second array of DRMs.
 18. Asilicon-on-insulator chip comprising: a first arrayed waveguide grating(AWG) comprising a plurality of waveguides in a plane, one or moreinputs, and one or more outputs; and a first array of detectorremodulators (DRMs), each of the DRMs comprising: a detector; amodulator; and a CMOS circuit connected between the detector and themodulator, the CMOS circuit having: a first external contact connectedto the detector and not connected to the modulator, and a secondexternal contact connected to the modulator and not connected to thedetector, the detector being configured to convert an input modulatedoptical signal to an electrical signal and comprising a firstsemiconductor junction arranged in the plane and the modulator beingconfigured to modulate an output optical signal using the electricalsignal and comprising a second semiconductor junction arranged in theplane; the first array of DRMs being in a planar arrangement with thefirst AWG such that the modulators of the DRMs are located within theplane; and wherein each DRM is located at an input or output of the AWG,wherein an input waveguide for the input modulated optical signal forone or more of the DRMs lies within the plane.
 19. Asilicon-on-insulator chip comprising: a first arrayed waveguide grating(AWG) comprising a plurality of waveguides in a plane, one or moreinputs, and one or more outputs; and a first array of detectorremodulators (DRMs), each of the DRMs comprising: a detector; amodulator; and a CMOS circuit connected between the detector and themodulator, the detector being configured to convert an input modulatedoptical signal to an electrical signal and comprising a firstsemiconductor junction arranged in the plane and the modulator beingconfigured to modulate an output optical signal using the electricalsignal and comprising a second semiconductor junction arranged in theplane; wherein an output of the detector is connected to an input of theCMOS circuit and an output of the CMOS circuit is connected to an inputof the modulator; the first array of DRMs being in a planar arrangementwith the first AWG such that the modulators of the DRMs are locatedwithin the plane; and wherein each DRM is located at an input or outputof the AWG, wherein an input waveguide for the input modulated opticalsignal for one or more of the DRMs lies within the plane.